I've started cycling again, maybe 4 miles on the flat four days for the first week, then throw in a hill for the next week and then keep adding a couple of miles per ride. Eventually I'll be back to the 2 mile flat, 8 mile climb and fantastic 10 mile desent home. Unfortunately I have lung damage and should I push it further than that I tend to get ill although I can do an all day ride if we stop or take it easy. I sometimes get pissed off when other cyclists sneer at my slow pace but untill they bring out a top with "I am sick dont laugh" on the back I'll learn to ignore it.
A couple of years ago I was at 16-20 miles per day, mostly climbs but as the weather got worse I started to cough up blood and catch cold every week. Still we can try.