Also...

Muscle mass generates T, and T stimulates muscle growth. As you age muscle mass naturally declines, taking some T with it...that loss of T further reduces muscle mass and so on.

Sustained weight training selectively targeting major muscle groups can help. No reason not to blast your biceps for vanity reasons if you want, but you need to hit tris, lats, pecs, and everything from the waist down. For the latter, deadlifts, calf-lifts, and squats will do the trick (deeper the better on the squats if your knees can take it).

Don't forget some core work to prevent injuries while doing the other stuff.

To be healthy you need at least moderate cardio too, but be aware that hardcore endurance training will burn muscle mass off and reduce T. Marathon or iron-man training would probably be counter-productive. If you're a determined hard-core endurance athlete, you might just need the shots.

Foods which contain zinc, or chelated zinc supplements can help too. Don't believe me? Buy a bag of cold-eze and take them for a few days and see what happens.

Benefit of all this is that you look and feel good, so can probably meet partners to help you enjoy your new-found vitality (as opposed to be being and old fat guy with high sex drive...).