They're succubi so their age is irrelevant to that of mere mortals.
But this whole fiasco is basically deciding if the chicken you've raised since a chick to become your next meal.
Well, if they eat him now, they only get the young shota flavor.
Imagine if they only eat a little bit, maybe on rotations.
Then they get the harem romcom protagonist flavor (a rare one, seeing as how most remains a virgin)
Then seeding oji-san flavor (can't imagine he'll evolve into any other variant)
Then maybe after 40s they can start preparing for the last supper.