PLZA spoilers, but I'm getting increasingly baffled by character ages people are throwing out and I think maybe folks just...aren't reading the dialogue.
I don't understand how anyone is getting the idea that Corbeau is like 30. Genuinely. It's indicated that (as with Gris) he was underage when Lysandre pulled his bullshit, which we know happened five years ago. Chronologically speaking, if we assume that the age of majority in Kalos is 18 (as in real-world France), he literally can't be older than 23. Corbeau calls the MC "kid"" in English, but to my knowledge it's only in English, and also I was personally calling 18-year-olds "kid" by the time I was 21.
Gris may be even younger than Corbeau, since he describes himself as being a child when Team Flare was in its prime, elaborating that he never actually did any "boots on the ground" work because he was too young by the time Lysandre went off the deep end. He's probably 20 or so. I get the vibe that Griselle is a bit older than Gris, and headcanon that she was the female Team Flare grunt in X/Y, just barely old enough for field work when things fell apart—which would explain why she's so much angrier about everything than Gris—but she's also second-generation Flare so she's unlikely to be older than 23 either.
For characters that people keep declaring to be younger than indicated in the game, the MC can't be a minor. Literally. They can't. The MC is supposed to be the same age as Urbain/Taunie—a character who was not only able to enter into a legally binding contract with the Rust Syndicate, but goes on to become CEO of a multibillion dollar corporation at the end of the game. Urbain/Taunie has to be a legal adult, so the MC has to be a legal adult.
Lida is also a legal adult. She lives at Hotel Z because she's studying dance in Lumiose on scholarship and could no longer afford rent when her roommate was scouted. This character is a legal adult. Judging by her behavior, I actually think she's the eldest of the group, somewhere between 19 and 21.
Naveen, though, is almost certainly still a minor. Just on the verge of 18, but not there yet—he still goes back to his abusive grandma periodically rather than living in the hotel outright, using a room there as a studio instead of a living space, but that isn't really definitive proof. However, he's the only member of the team who wasn't contacted by the Rust Syndicate about the debt. If he's a minor, he can't be held under contract, which would explain why Philippe and Corbeau never contacted him. Naveen is probably 17.
Lastly, Team MZ owns and operates Hotel Z after the main storyline. This would not be possible if they were a bunch of children. Naveen will presumably turn 18 in the next few months, but Urbain/Taunie, Lida, and the MC are all legal adults.