This is interesting because we had a discussion on this on our Sat. ride. I asked if there was a point being 57 years old that you could no longer improve on speed and climbing, etc. Another guy made a good point that as you improve you tend to ride with better riders and are still dragging up the rear so you feel like you have not improved. He said think about the riders you rode with 2 years ago. Today you most likely would drop them in a heartbeat. So improvement is slow in cycling and that improvement may not show up so easily.