And the best weight by far to lift - your own weight. Our bodies are naturally designed to work with this weight (unless you are obese), our joints and connective tissue is literally built to match it. If given movement becomes too easy, just slow it down, add repetitions, modify slightly and voila - challenge is back.

Sure, with weightlifting you strengthen everything including those joints, but only to certain amount, and road there is full of booby traps in form of variously crippling injuries. Look at powerlifters, how much joint protection they need just to perform, and look how they look retired (if they are actually still around, most have massive weight issues). People who consistently want to look like Arnold and actually execute it have often some deep childhood issues they are compensating with working out insanely (and taking various chemical crap that bites back later to stay on top).

Being lean, have decent power and endless stamina is literal heaven for everything you ever wanted to do - work, longevity, sex, confidence, happiness, women love it. Supplement it with moderate weights, for sure, even include them in workouts (ie in nature hiking with heavy backpacks with camping/climbing gear is amazing). Or weighted squats in very good form. But only once you built a very solid base in joints and connective tissue with easier stuff repeated a lot, for some time.

Patience as with everything else is the key to long term performance. And discussed longevity requires decades of consistent efforts.

Or do it like my grandparents, both lived till 95 - have a decent garden with various fruits and vegetables, take proper care of it daily. Just find something to do in winters too (ie ski touring). And no vices ala alcohol nor cigarettes.