You know, this is slightly off topic and I still think it technically counts as spoilers but I always found this funny as hell
Anyway, rant over. I just always found that premature aging amusing
Yeah, with these Yautja, it's certainly seems like it's not the age but the mileage. Excepting some of the books which I haven't read, the oldest Yauts we appear to have seen have been Kalakta who, as you've pointed out has at least a 974 year span that we've seen. We can assume he's fairly young in that first appearance, and yeah, he's probably seen a lot of action between his first and second appearances, but he probably has that Steve Martin/Patrick Stewart silver fox thing going on as well. From the culture bits that have
been shown in the EU, many of the clans seem to operate on a meritocracy, so youngish clan leaders are certainly plausible and likely. There have also been hints about royalty and revered bloodlines out there too, so if their cultures are at least
as diverse as ours, which they should be, it can be assumed that there might be a Shia & Sunni kind of dynamic going on, like factions supporting merit vs birthright. But anyway, I digress...
The other eldest we've seen are that crusty Shaman dude from Homeworld with the cricket protector looking mask. These "Homeworld" guys are really interesting because it seems like the elder is some kind of preacher on a mission to save the youth of some backwoods green-trash clans, likely descended from the banished, the isolationist, or otherwise disgraced from greater pred society. These teenage hooligans appear to have succumbed to the charms of space-satanic ritualism, and the yautja-sacrifice that inevitably goes along with it, and our preacher/shaman elder has to go hunt down the worst of wayward punks and nip some badbloods in the bud. There's a lot of ambiguity in Homeworld and I kind of love it.
The oldest and most haggard elder we've seen has been Old Dragon from Predator Xenogenesis and his 1000 year battle with Subotai, we have no idea how old he was when he started their feud, but we've seen a lot of youngbloods cutting their mandibles on Earth, so it's possible he could have been fairly young as well at the start.
So nothing definitive has ever been stated, but on average it seems like a factor of 10x years can be applied to Yauts as compared to humans when it comes to normal-ish life spans. But science and alien biology is a hell of drug so there's always wiggle room for statistical outliers.