Depends on health issues as much as anything else. A friend is in his early 70s and can still ride his age if he's motivated to, although usually his rides are 20-40 miles.

At 60 now, in the third year since I resumed cycling in 2015, I've ridden a few metric centuries -- around 62 miles. Those generally got easier as my conditioning improved. The first in 2016 on my one year anniversary of resuming cycling was difficult. The next year was easier. This year was easier still, up until a recent injury.

But chronic neck pain from a 2001 wreck and now a shoulder injury from being hit by a car in May have limited me in some attempts at rides longer than 50 miles, and have limited me to one full century, last fall near my 60th birthday.

I tried a recumbent loaned to me by a friend but couldn't get the hang of it. So I may need to consider a less aggressive road bike with the handlebar closer to saddle height and the more ergonomically friendly brifters and frames of some touring or adventure bikes. I have a hybrid with a comfortable frame and flexible fork that soaks up most road chatter, but the single position flat and riser bars limit hand positions too much and become uncomfortable after 30 miles or so. I may modify that bike to a drop bar.

Meanwhile I'm putting time in on an indoor trainer to maintain basic conditioning, and limiting my road time to once or twice a week -- mostly for balance and heat adaptation. Fixed indoor trainers like the Cycleops don't help reinforce balance and basic bike handling. While rollers might help I'm not motivated enough to clutter up the apartment any more than it already is. My shoulder has improved enough to cope with one or two rides of about 20 miles a week.