I think it's interesting to consider in evolutionary terms: "what's the tradeoff?"
Why is there the proportion of Methuselan species that there are? Why not more, or less?
One simple take is old age is adaptive: the longer you live, the more chances to mate, the more offpsring, the more likely that your genes survive, perpetuating it.
One simple counter take is old age is not adaptive: the longer you live, the more your learned skills (or "maturity bequeathed survival" in the species where it's hard to say they are learning something), permit you to steal resources from the young, lessening the chances of survival of all offspring, on average. (you may take issue with that implication but you can also see how it is true, or better yet come up with another counter take!).
A second simple counter take is each generation lives longer so there's less evolution.
I think that in a species that learns, has a big brain, and is already adaptive, it makes sense that it will try to live longer because it's primary survival advantage comes not from its evolutionary legacy but from its accrued learnings (one may dispute that, or get pedantic and say "but without the original evolution you couldn't have the accrued culture", but you can also see how it's true), so even tho it's not "evolutionary"-based adaption, it's "self tinkering"-based adaptation. The longer you live, the more you learn, the better your chance of survival. Even if not evolutionary, you "Beat the gene", and make your culture, (and yourself, and all Methusalan individuals in it) more likely to be alive...rather obviously I guess.
So if we do come across aliens from such a species (like us, or orcas, or other big-brained, learning species, but more advanced), then it's likely they live a looong time. Unless they got fussy about some ethical issue with doing so, and decided against it. But any ethics involved seems unlikely to be proscribed by a constraint on energy capture / resource usage...as that would likely be one of the other characteristics of such a civilization, by virtue of us having been able to encounter them, it seems they were already able to master that. So it's highly likely that they live a long time.
So maybe, those "longevity gap" situations that people are so fond of agonizing and preaching about...are already the case on a cosmic scale, and the present race of humans are currently the beneficiary of the "less fortunate position".
Interesting to think tho, has the first child been born that will be the last generation to face death?
I'm reminded of two verses:
Old age should burn and rave at close of day;
and
Age shall not weary them, nor the years condemn.