Keep on Riding -- Use It or Lose It!
I'm 64. I learned to ride serious bikes in 8th grade when I started longer rides on my Dad's fixed geared with wooden rims that had belonged to a great Belgian champion in the 1920s. I still have that bike and ride it on occasion.
My other favorite bikes are two Italian road frames: A Rolls (read Colnago) 1974 criterium bike with 10-speed Campy that I learned to race on in college, and which I converted to a fixed gear about 16 years ago. And a Mondonico stage racing frame (all Campy, of course) that I bought in 2001. I also have a 1995 Cannondale aluminum touring bike that I use for trails and local fun rides, but most of my workouts are on the fixed gear or Mondonico. As you can see, I love the traditional Italian steel frames with classic Campagnolo; I've tried some of the titanium and carbon bikes, but would not trade my Italian steel frames for them, even if the newer bikes were free of charge.
The keys to being healthy and fit in your Sixties are a) riding regularly, b) keeping diet, alcohol, weight, sleep patterns, etc., in moderation (I've never latched on to any fad diets or jazzy commercial exercise programs), and c) adding in other fitness activities and workouts, such as hiking, running, climbing, cross-country skiing, swimming, calisthenics, and moderate free weights or gym machines. I'm not competing and I really don't track statistics or total miles, but I'm cycling and adding in some of the other activities several times a week, and I've been doing these for about 50 years now without any major break.
I like fixed gear with tubulars because of the fun of "slalom" turns on open roads and cul-de-sacs, and because the fixed gear provides such a great strength workout for all the leg and lower core muscles.
I have to admit it's fun when I quickly pass people in their Thirties or Forties on a hill and they yell out something about "how it must be nice for you younger guys to be able to ride so well"!
So, for all of you who really are young (i.e., less than 64 years old), keep on riding! Use it or lose it!
Mike