I know we as a fandom have decided to ignore the weird werewolf aging but I can’t help but think about it. The fact is at this point Stiles will age and die long before Derek (or any of the other wolves) will die. My way around this is by headcanoning that he is some sort of supernatural thing (which there’s a lot in canon to support this) and whatever he is alters his aging so he ages as weirdly as the wolves do. Or my other headcanon is that Stiles is 30 he and Derek have like 3 kids (all werewolves) and it hits him that thanks to the aging one day he’ll leave them all behind. Of course he doesn’t want that so he decides to finally take the bite and become a werewolf too.