The YJ kids were *never* 11 as sidekicks in the comics. Even the youngest-at-intro (Tim) was introduced at 13, and the others were 14/15. Though certainly the all-too-often de-aging of heroes annoys me greatly.
19, generally. Though it was (stupidly, IMO) retconned to 16 (I believe during Nightwing: Year One, but definitely during latter post-COIE days when they decided to de-age Dick to 21 in the present-tense).Tim was like 17 when he had to give up Robin. How old was Dick when he had to give up Robin.
I don't think it can at all be undone, but I really do think there are negatives to what they did. Back before Jason, being Robin wasn't something one "graduated" from - Robin grew up with Dick and was an adult hero and widely respected as such. Now it's become a transitional/"kid" role, and I don't like really like it (thought I absolutely accept it). It's even worse that they then did the same with Batgirl. I'm not a legacy fan, anyway (I like the idea of characters making their own names great, not having the height of achievement being handed someone else's), but this sort of led to the idea that all teen heroes have to shed their identities to "grow up." I can see doing that with names with "kid" or "boy" or "girl" and whatnot in the title, but not for Impulse and the like. There's no reason he shouldn't keep that name, that's **his** forever. And Nightwing, especially, should never be a legacy given that the story on him taking that identity specifically to disassociate from the established hero.
And same-naming them makes it more likely for fandom in-fighting, displacement of pre-existing characters, and then even the writers crapping on the others that held the title (or at least specifically and intentionally diminishing them to make the one look superior to the rest).