I'm three years older than you, and did about the same thing 12 years ago. If you have some athletic experience (I was a runner for 20+ years), you already know the phrase "listen to your body." it's usually recommended not to add more than 10 percent a week to your mileage, though that seems less rigid in cycling than running. I've never had a cycling injury except with a fall, and I was always sore when I ran. Fit and setup are important, but the "right" way you read about in books is often aimed at 19-year-olds and racers. Us geezers may need the bars higher or closer or whatever to be comfortable. Some people, even in bike shops, will urge you to force yourself into the pro position. It IS a little more efficient, but if you can't hold it for more than 10 minutes, you'll probably lose in the long run. Don't be afraid to experiment.
You don't have to abandon flats to ride on hills. Just add a climb now and
then, push yourself occasionally (insert traditional warning about consulting a
physician before beginning an exercise program here) and take a rest day, or at least an easy day, once or twice a week. At our age we can get faster but not fast, and it's more important to me to be riding at all at age 72 or whatever than to be riding fast at 67. If it's not fun, why bother with it?
There's at least one book on this, called (I think) Cycling Past 50, by Joe Somebody, that was helpful to me. I have it upstairs but I'm too lazy to go find it...
Last edited by Velo Dog; 06-02-12 at 10:56 PM.