Some questions:
Please tell us your age.
1. What type of bikes do 50+ folks ride?
I ride an '05 Specialized Dolce comp & am stoker on an '06 Raleigh Coupe tandem.
2. Do you take any special supplements/vitamins/minerals as you have grown older?
Glucosamine/chondroitin, extra Bs, calcium, and a decent multi.
3. How much do you feel you have "slowed down" if any?
Slow down? What's that? 
4. How long have you been biking? New, around a while, biked all your life?
Mostly my whole life, off and on, mostly road. Tried mountain biking for about a minute & realized it wasn't for me, so I'm a roadie all the way now. In Aug. '05 I rediscovered my love of the road & there's been no stopping me since.
5. What type of biking do you do? Long rides, touring, short rec rides, commute, tour, race?
I try to do two club rides of about 30 mi. each week. Otherwise I favor centuries, am leaning toward double metrics (and beyond...?), am going for my first time trial ever on the tandem in a week. 
6. How often do you bike? Your approximate annual mileage?
Every chance I get! Mileage varies depending how busy I get with work (self-employed). Last year I accumulated over 4K between the Dolce & the tandem.
7. Do you do any other type of physical activities - weight lifting, skiing, running, etc.?
Weight training/Pilates-type work a couple times a week; running, swimming, Jazzercise when I can't ride. I teach 2 Spinning classes a week just for grins.
Perhaps you might indicate your age on your reply??
52, although I neither look nor act it.
Also, please see a list of all the contributors: