I resonate with this, but it does imply "pay it forward"-esque mechanics for longevity.

I disagree, it really just gets easier the more you do it without expecting anything in return. If you feed on gratitude or reciprocation, that's your reward. If you don't, but rather do it purely because that's the kind of person you want to be, it becomes as natural as breathing. You don't think about it anymore

but there is only so much energy one can give to others, and it's hard to multiply what little kindness you receive, sometimes. For me, the question is "how can I replenish that energy to continue to be the good person I want to be?"

I think there's a really easy answer... You give what you have to give, and just a little bit more. Like exercise. You push yourself but don't run yourself ragged, you rest and recover. When you have the energy you seek out opportunities to use it, when you don't you conserve your energy to recover, but still make an effort to do the little things

I find that that's when other people tend to show concern and try to help me in turn, although if you expect it you're probably going to be disappointed

All that doesn't just make you a good person, it also makes you a genuine one