I am 65yo, a life long cyclist and competitive cyclist. No, I am not as fast as I used to be, not even close. But I maintain myself and keep weight down, 5-11 and 156 pounds. Weight off me is way better than weight of the bicycle. We do a weight watcher based diet, I restrict calories and eat very little that is not essential. But I am still pretty fast and can put on a turn of speed when needed.
I do not cycle big miles but I workout every day. I swim and I do weights and I run (elliptical mostly) and I cycle. I see too many older cyclists with a spare tire around the middle, they have a good engine still but they are hampered by way too much extra weight. Getting a CF bicycle is not going to make up for that. Weight around the middle is the worst place for a man, restricts flexibility, breathing and heart/circulation. I swim more in the winter and cycle more in the summers but do all four throughout the year. It is absolutely essential to keep the weight down/off to go fast on a bicycle.