I qualify as a 66 year old. Don't feel that I have much to contribute to these forums but I sure have enjoyed reading the 50+ forum in the last two years.
I've been cycling for over 35 years and it is the biggest factor in maintaining my physical and mental health at levels that make me feel far younger than my years. I don't worry about equipment, techniques, clothing etc. anymore, just about getting out there and improving my fitness level on a continuing basis.
I'm sure most of us at this age would agree that health and fitness, along with the fun of being out there are the biggest reasons we've stayed on the bike when far too many of our friends have become "couch potatoes".