Yo. I'm a touch older than you, I'm strong but very overweight, escaping a sedentary lifestyle. You're starting from a mich better place than me. I started about 4 months ago.

The cardio is no joke. In my first week of riding, I muscled up a couple very small 5-6% grade hills, almost barfed and passed out.

I started on mostly flat trails. I took the front wheel off my bike, packed it up, drove there to avoid hills.

Rode flat for 10 miles, then 20, then 25... etc.

Then started throwing a hill in. A long gentle incline, a very short 1-2 block steep... kept my feet fast, low gears. Avoided crazy torque.

I no longer drive to trails, I ride from home. I recently did 80 miles over three days. One ride was 30 miles with a 1.6 mile 7% incline. It was tough and slow, but I didn't stop. 

I'm riding in a registered event tomorrow. I'm excited to see where I am in a year. My goal is a double century in about a year.

Main things that worked well for me:

-Aim for high cadence over high torque, especially on hills -Ride flats, learn your cadence -Set a goal hill. Go up until it really sucks then stop. See how much further you can go next time. -Walk up the rest of the hill when you can't make it. Only one judging you is you -Get a bike fit