Here is a secret from men with strong manly erection at 70! (From My old neighbor at 78 who still bang like at 20. I buy condoms for him).
Exercise when you feel tired already.
When you feel tired, go for a 5km walkout.
Or go to your nearby Gym.
Rest only when you feel good.
Don’t use any manly enhancement drug, unless you have a disease.
Exercising when tired make you look younger and more vigorous just after a week.
Don’t trust me on this. Try it and report here.