I at 80 today, never believed we're made to weigh ourslves, count calories, and still have been always able to maintain a reasonably fit body to get thru my work and play.
How does it happen?

I plan what I need to accomplish in my day or weeks that would help me get to achieve where I want/like to be in life. It's the GOAL in life, aka Purpose, that steers my time use. I know it's best achieved in a reasonably rested, strong, fit and alert body. It's purpose that guides my life...as do many others who follow their north stars.

Today I can walk up all 13 floors in my bldg huffing puffing the last six. It's a good feeling; no counting/watching floor numbers as I walk up. It's more interesting to be Within one's body. If body says Enough, respect it, why otherwise?

Just eat a sensible diet -- I am sure CDC and Harvard health and the like have plenty on it. Do play-pullups/push ups, kicking an imaginary soccer ball hard enough to get your heart racing in One minute. Make exertion play. Invent!

You will sleep better. And yes surround yourself with friends who laugh with you and also Challenge your opinions. You need a working fit mind. Life is to GROW.

Good luck.
It seems to keep me without any doc visits, meds, tests, surgeries or even calls.