I recently rode alongside an elderly gentleman. We were both moving at a decent clip. He was riding into the wind on a fixed-gear bike. He said that he was 80 years old. ... born in 1929! The quotes I remember were: 1) "I have lost some leg strength, so I try to keep my weight between 134 and 136." and 2) "I'll never get off my bike." How's that for some inspiration! Maybe it will help answer your question.