I'm 40 and I can confirm that the biggest age related change that affect my performance is recovery. I lift weights since I was 20, and that has been my #1 sport until COVID when gyms were forced to close. Years ago I used to train 6 days a week, but that frequency was reduced to 4 days a week since I was about 38. Since COVID I just train at home 3 days a week with very light weights, so my performance in the bike has improved, a little, I recover enough to ride faster on weekends and I´m 5 kgs lighter since I dont lift heavy enough to keep the extra muscle I had. I also managed to sleep better and more, I used to have 6 hours of sleep and now I have 7-8 hours, still not enough sometimes, but that helps a lot with recovery, no coffee after 12 pm and no bright lights in my home after 8 pm.