If you don't have energy at 40 it's not because of your age. You can win a championship in any major sport at that age.
If I hadn't kept fitness and eating healthy as a priority for the last 15 years, my health would've been in complete shambles by now. I was pretty lazy and self-destructive through my early adolescence, and in my early twenties I was in terrible shape physically and had a lot of severe mental problems that I no longer struggle with. I'm extremely grateful to my 22-year old self that decided to try and turn things around, it didn't happen overnight.
As for me, I have vasomotor rhinitis since I was 34 because I lived in a street full of cars and air pollution when I was young to save on rent. Now I'm full of money that I can use to decrease all the bad effects that the sickness has on me (like going to hotels far away from cities/villages), but I won't have a normal life until my methylation levels can be reversed.