Don't let the naysayers in this thread get you down.
The best years of my life have been from 45 onwards.
I'm now fitter, healthier, leaner and happier than I was in my 20s and 30s. The reason is simple and it is because I got my priorities right after periods of confusion and self doubt in my younger years.
And the notion that sex will invariably go downhill is absolutely false. In order to function well sexually there are two essential elements that need to work in tandem and they are your testosterone levels and your artery health and both these aspects of your overall health can be taken care of with just one activity which is regular exercise!
If you ask me today what is the most important activity that I perform as part of my regular routine it just has to be my daily workout.
Why else do you think I constantly try to get commuters out of their cars and into cycling. It's because it will transform their lives immensely with far better outcomes than winning Toto.
If you need more detailed information just let me know and I can point you in the right direction.