I've found stretching to be unnecessary when coupled with a well-executed weight training program. The program itself, with the lifts done for the full range of motion, will be plenty of stretching. That said - up until it isn't enough anymore. I had to start stretching at about 65, probably because all that stuff becomes less flexible as we age. I started running into bursitis issues which resolved with stretching. If one isn't having issues, there's good research which shows that stretching beyond the range of motion required by your sport can lead to injury, the opposite of what people think it will do.

Riffing off the above, certainly what is required for continued excellence in your sport will change with age. I see a lot of riders with back, nerve, and tendon issues. Most of those resolve with targeted weight and stretch training. For instance, I have acquired a tendency for impingement in my shoulders. I keep that at bay with a specialized exercise/stretch.