So the tl;dr from what I've found so far is that:
* What you eat
* When you eat
* How much you eat
* Exercise
Are by far the simplest, cheapest, and most well documented way to extend life by quite a lot. We have lots of evidence to back calorie restriction. We know that eating more earlier in the day vs later means your insulin levels can recover better (or something?). We know eating certain types of fats is bad for you, and eating certain types of other things are good for you. Exercise, or at least the right kind of exercise (seems like there are open questions here, like how much is actually important) is healthy.
Then there are a number of pills you can take. When it comes to the pills we have a lot less evidence. From what I've seen there are probably a dozen or so pills, each one with bits and pieces of science surrounding them, that will maybe have some impact on mortality or aging. Some of the research does seem quite compelling - niacin, for example, seems to be pretty well researched and is actually prescribed at times. Niacin is also one of the pills you'll see come up a lot if you start looking into anti-aging. Others like resveratrol (which, actually, appears to be old news - people have moved on, it seems, to more bioavailable substances) have a lot less research, though they're promising.
If you're willing to spend 100-200 dollars a month or so it seems that you can get most or all of these. I don't think any research has been done on what taking all of these will do to you, but there is research on how the chemicals behave and I suppose from there people seem to draw conclusions on interactions.
Interestingly, from what I've read a lot of the popular "anti aging" trends like anti-oxidants are, more or less, very much debunked. My understanding is that while anti-oxidants absolutely do what their name implies in a lab setting, most of them tend to not do a damn thing in humans with regards to oxidation. So who knows what is or isn't going to work.
From my layman understanding, if you're ~20 years old you can basically just not fuck up super hard and wait another decade and we'll know a lot more. If you're 30, definitely start taking health seriously but maybe don't worry so much about downing 50 supplements that only have a bit of backing research. If you're 40 and above, and your goal is life extension... you might have to take a gamble.
If you're interested, I found this channel quite interesting - I appreciated the guy always citing studies (and he explicitly calls out why he thinks the study is or is not high quality).
https://www.youtube.com/channel/UCpcvPcHJVOkO9Qp79BOagTg
This FAQ definitely seems to be a good 'one stop shop' for learning the state of things, without being prescriptive.
I'm not a doctor. I just got interested in the last few weeks about this stuff. None of this is without risk - that much is obvious. Only just the other day I was reading a post by someone who ended up in the hospital with liver failure that very possibly could have been tied to their supplementation. If you start taking pills that you don't understand you seem very likely to fuck things up - some pills require that you take other pills also, for example lots of nootropics will fuck you up if you don't get enough choline in your diet. All of this is to say, there's cool and promising stuff here, but do your own research, and if you're very young and healthy don't stress about this stuff yet - the first step is always diet and exercise.