until I read some of these posts.
I started out pretty much where a couple of people have indicated they were - unable to go a mile with getting winded and stopping. My lungs were giving up first but my legs weren't much better.
Over a period of a six weeks that improved, by riding every day. At first I forced myself to go two miles (around the block twice).

Having started work at distant job site (no possibility of biking for me there) I started riding Saturdays and Sundays and during the week, using the hotel gym/pool to ensure I got regular exercise, even after 10-11 hours of stressful work.

But my weekend rides (when snow an temperature allows now - I live in NH) are between 12 and 15 miles. After a ride like that, I rest for a while.

It's nothing to brag about, but it has made a world of difference to me. I can take a steady stream of 10 hour days and still have energy and clarity enough to focus on my own interests at night.

Soon the work will be done and I will cease making these trips, I expect to continue to improve, but I'm very happy I started doing this and didn't quirt when it got cold.

I also have a trainer now (Santa Clause) which I've used 3 times, so I don't necessarily need to go anywhere to sweat and ugh for an hour at a time - which suits me fine.

... still working on my success story (60 years old and haven't been in shape since 25 years ago).

Rich