I read that in the core worlds, the Reavers from Firefly/Serenity are legendary (campfire tales or something), so it sounds like they have been around for a long time.
They must get killed frequently and die from various other things like radiation and lack of medical care. I read that some humans might be converted if the the reavers detect some genetic difference and this process is no doubt unpleasant.
Is there any evidence that they also reproduce naturally, with offspring of two Reavers becoming Reavers themselves? Or perhaps they bring up children (not necessarily their own) who at least sometimes grow up to be Reavers or at least fake it? (Interesting story idea, Reavers who despite looking like the rest, want to escape to a normal place - maybe someone has written that already?)
We know that they can fly and maintain spacecraft so they are not mindless, so mating or childrearing seems plausible.
EDIT: Mine it turns out is sort of a dupe of a question about whether Reavers have babies and someone asserted that, No, they don't have little "ragebabies." But do not giant hornets, sort of like Reavers to bees and other species, not raise their own young and in fact raid to feed them. A story showing this paradoxical-seeming thing among the Reavers would be interesting: perhaps there is a caste of less-violent Reavers who take care of baby Reavers, member of this caste having to protect the babies from other Reavers and also protest themselves from random violence. At the same time, such young Reavers would grow up in an unbelievably violent environment (I believe hornet colonies are much more violent than bee colonies in terms of intra-colony violence. Wasps fight with each other to establish hierarchies that are remembered -- bees do not beyond expelling useless males, not really fights.) sort of like street urchins in Oliver Twist or something.