Early last summer I was doing the same thing as OP.  Got an electric bike, decided to ride to work once a week.  Then it was twice a week.  Problem was, I didn't feel like I was getting stronger.  In fact, it felt like I was unable to keep up with the oxygen demand as the ride progressed.  Towards the end of the rides my chest was starting to burn.  

I backed off, stopped riding.  Turned out I've got a 100% blocked artery in my heart.  

Go get a stress test done OP.  Talk to your doctor and get one scheduled.

Play it by ear. Ride as much as your legs and schedule allow, and or look up some training programs/apps. Mixing it up with some walking and strength training is ideal. Squats and pushups are simple, and don't require any equipment. Stretch and cut back on sugar/carbs.

We have a ride thread in the bike forum, join in, I know seeing what other people accomplish motivates me.

I admire you for posting this.  Diet is very important.   What are your health/weight goals?  Have you spoked to your Physician?  At 52, going from couch to bike could bring on a heart attack.  
What is your blood pressure?

Ozempic will make 30 pounds just fall right off of you.   Getting down to a 34" jeans is attainable with diet, exercize and help from a weekly shot.

Get a Yunami scale off of Amazon that measures body fat.

Have you been in to see your doctor?  If not, it would be a great idea.  They'll probably want to do a bunch of blood test.  Screening for diabetes or thyroid problems.  Check out your heart like a previous poster said.

My wife's cousin was about 80 pounds overweight and went into a serious diet and exercise program.  Dropped a bunch of weight and dropped dead at the age of 37 at the top of a hill on his bike. Left a wife and one-year-old boy.  

As far a diet.  Never drink another sugary drink again.  Sodas, sweet tees, and fruit juice are absolutely terrible for you.

Walk.  Walk every single day.

Pick all the low hanging fruit first: sugary drinks and sodas, candy, desserts, too much beer and completely sedentary behavior. Simply more daily movement and eating more mindfully is the start.
Start tracking what you eat and get an honest appraisal of how much and what you eat.

At the macro level, it's calories in versus calories out. All dietary approaches whether Keto, Carnivore, Intermittent Fasting, OMAD or simple calorie counting are ways to prevent excess caloric intake.
They all work.
The elephant in the room is that eating, satiety and nutrition have significant psychological dimensions that are shaped by upbringing, socialization, work schedules and simple convenience.
So you have to find the approach that works for you in your life as it is now. Find your energy balance: your basal metabolic rate (the number of calories your body consumes simply functioning day to day) and use that to construct an eating plan.
From there, the goal is to both decrease caloric intake gradually, no more than a pound a week, or 500 calories a day,( even less is fine if it's consistent over time) while at the same time increasing activity gradually. Together, they will begin to make real progress within a matter of weeks. You don't want extremes of calorie restriction or increased activity because lack of adherence over time to either is the reason for people quitting.

Also, to put it as kindly as possible...you ain't a spring chicken.
You hit 50...50 hits back.
You should absolutely begin exercising, both a weightlifting and a cardiovascular training program.
Slow and steady, always showing up, with a real eye on avoiding injury-even at the expense of "gainz", will be needed to do this for the rest of your life. You're not under a time crunch to get ready for a contest, a season or a show. A lot of programs are, consciously or unconsciously, constructed around the idea of maximum progress in minimal time.
Many of them have the baked in acceptance of injuries as the price for excellence.
That's fine for an 18 year old football player or a 25 year old soldier preparing for Selection, or even a 30 year old who has run and lifted his whole life and wants to take it to another level.
But that, unfortunately, is no longer you.
Exercise is mandatory...but no one exercise is mandatory. Only certain sports have required exercises. If you don't like a given exercise(no matter how "optimal" it is), don't do it. There are endless substitutes that accomplish the same outcomes.

You(like all of us over 50) are now locked in an existential battle against All Cause Mortality with the goal(presumably) of extending not you lifespan so much as your healthspan.
Being 100 pounds overweight is, in its way, an accomplishment. It took many years, probably a couple of decades, to get there. Reversing it, and the accumulation of lifestyle behaviors that enabled it, will take effort and application over time, an extended period of time, frankly.

But this time next year, with almost no effort you could be 40 or 50 pounds lighter and feel a Hell of a lot better. Add in some real consistent effort and gradual lifestyle changes and you could be closer to 75 pounds lighter, in much better cardiovascular and metabolic condition, and a lot stronger.
In 2 or 3 years you could have the biomarkers of a 30 year old in good shape..and stay that way into your 70s.

Ride on flat ground if you need to for a while.  You can do some walking with weight on your back, esp. up/down hills to help with leg strength.  
Make a schedule and stick to it.  Cut down on the shit food too.  

Don’t make goals, make habits.  Ride the bike 5 miles every other day(or whatever) for a while.  After a month or three reevaluate and update your habit as necessary.  Goals are worthless without a way to achieve them, the habits you make are what keep you moving towards where you want to be.

I’m not much of a fast food person,maybe a Wendy’s burger once or twice a month. We mostly cook and eat at home. I need to stop cooking pasta & eating bread,rice etc.
I only drink water with and occasionally a  soda.
I work a full time job & a part time job with only one day off a week. If I didn’t have the part time job I’d have 3 days a week off.
I go to work,come home sit in recliner and sleep. I really let myself go all these years. I will take the advice of starting out every other day and work up from there.
I will also call my doctor to make an appointment. I do have high blood pressure and I’m taking lisinopril and it’s keeping pressure at a low level.

Others already here gave great advice...

Of someone who used to ride bikes (for hours), I think OP is being too hard on himself for just starting on a bike. You have to build up strength/tolerance and be using the right gears, etc.

That being said, like others said, start slow and build up and definitely look at your diet.

The thing is to not stop moving.

One of my favorite YouTubers, she just did a post about losing weight after her 2nd child. No, she wasn't doing the hour, 40, 30, etc. min videos that she used to do, but made sure she consistently did at least 20 min, 4x a week and has lost a lot of the weight...so keep moving, even if it's a walk around the block.

https://www.youtube.com/channel/UCZUUZFex6AaIU4QTopFudYA/community?lb=UgkxZXqx0i92wcRdesCIGEAmOd68DwdbBQU7

Start off slow, both diet and exercise.

Anything too extreme you’re going to be hurting too much to continue

Start off cutting one thing you eat that’s terrible for you progress from their

Ease into the workouts. Give your joints and ligaments time to adjust and strengthen.

This.

As far as riding, I'd suggest making time for it daily but only pushing yourself a little. If you haven't done this in a while/ever, just establish the habit first and build on it. Strength training in some capacity alongside cardio for fitness is a well-established and often recommended approach as well, so the weights are a good idea. Diet and lifestyle obviously go right along with all this, and the posts about seeing a doctor first and being careful with your heart seem like a really good idea. I'm just old enough to start needing that advice but still young enough to be too stupid to follow it so I'll defer to people who've been there on that one

That’s no shit though. It sneaks up on you. One day I stepped on a scale and realized I was 40 pounds heavier than I thought, and I was disgusted. I started my diet the very next day and the rest is history.

This.  If you have a rail trail nearby those are great places to ride because the inclines are gradual.  If you ride regularly you will get stronger and it will get easier.  When I first bought my mountain bike I could hardly ride a trail without feeling like I was having a stroke.  Within a couple months of regular riding I found it much easier to ride the moderate trails.  Two surgeries and a job change with a long commute later and I'm back to square one again.  Keep after it and you will get there.

As many have said, start slow and short.

Do a few easy miles 2x per week for 2 weeks

Then up the distance by 1 mile and and do that longer distance 1x per week but keep the shorter distances so you are riding 3x week.

Slowly up the distance once per week and make last weeks "long" ride this weeks short ride.

Do this until you get up 10ish miles then have at it.

Best wishes for success, OP!

52 is a good age to turn things around. I did that at 52 back in 12/06. My doctor scared me in telling me that I was pre-diabetic.

I lost 72 lbs by 8/07, 80-90 by end of 12/07.

Kept it off for 5 years (was diagnosed with prostate cancer, had the surgery) but let some come back, yet I still fight the good fight.

What helped me was allowing myself to eat whatever I wanted at supper one night a week (Started on Friday nights, then added Friday and Saturday). Also, I started slowly but after about 6 months actually got psyched up to put things in high gear (lots of salads and fewer carbs). Also walked in the early mornings or evenings 2-6 miles each day.

It's a game of understanding one's own psychology, IMO. Good luck!

This. Snack on carrots. Avoid sugar, go easy on carbs. Avoid alcohol. That's what I do. I'm also 32, not 50, so that helps.

Former bicycle mechanic here.  I'll tell you watched a lot of people get back in serious shape just by riding consistently AND monitoring their diet.  I'm not saying weights won't help.  But it just depends on what kind of shape you want to be in.

Someone else on here said that you didn't get that way overnight and you will not get better overnight.  That's truth.  You gotta stick with it.

It took a while for you to get in the shape you're in so give yourself time to change. If it was me I would start slow but make a habit of doing 15-20 minutes a day at the same time if possible. The habit is more important than what you accomplish. It takes the body about a day per 10 years old you are to adjust to changes in exercise so it will take you about 5 days to feel acclimated to your new routine. I wouldn't push it for the first 5 days-learning the routine, learning to detox (sweat/strain) is plenty. Every week add either speed or time. Drink lots of water and get plenty of rest.

good luck!

One step at a time.
Everyday do more exercise than the day before up to your max limit.

Eat proteins and veggies only, no fruits or anything that tastes sweet.
Drink water only.
No bread, no pasta, no rice, no potatoes.
Nothing with any amount of sugar in it, those are the worst of the worst.

I am an out of shape 52 yo as well. Not really over weight and not totally out of shape, I am not a fitness expert either.

I would go to your local school that has a track at night. Force your self to do the track, 4 loops is a mile, do it 3-5 days a week. Week one and two walk a lap, ride a lap and walk two more. Every week add a lap on the bike, so week three is walk one, ride two walk two. Once you get to 3 laps on the bike, do the middle one at a higher pace. Eventually lower the end walking laps to one as a cool off.

This gives you an easy to track goal of time and numbers of laps, gives you a warm up and cool down every time. You can increase and decrease the number of days a week depending on how you feel ( soreness etc ), but do it at least 3 days a week.

You will find it will take about 4 mins a lap to walk it, and 1.5 mins on the bike at first. Over time you can decrease the time per lap on the bike, as you do more laps, but the over all time should be similar. Maybe even start walking faster and maybe even a jog for some or all of a lap as your body allows.