The Wards are not defined by the majority/minority of the members, but by their age. That said, I imagine the Protectorate IS defined by the majority/minority status of the members.
It could go any of three ways:
The second is the most likely if their power is genuinely useful enough and they show enough maturity and responsibility to be trusted to do the serious police- and hero-work that is required. They are, essentially, emancipated minors signing up to be cops. As parahumans, they're desirable for that role despite any physical immaturity, but they'll be expected to be at LEAST as mature, on the job, as their coworkers. This would be especially true if, for instance, they needed to make a living at this. Being emancipated, they would need to support themselves, after all.
The first is almost guaranteed if they're too young to "pass" in costume as an adult. The PR of having an obviously underaged (even if they gave out such identifying information as "Magnificent Lad is an emancipated minor") hero who was taking on real Protectorate jobs would feed way too fast into "child soldier" narratives that the Wards program fights tooth and nail to let the PRT/Protectorate avoid. And you know the Youth Guard, being not technically a government agency and thus peopled by volunteers, would ignore the "emancipated" part and focus on the "minor," and try to insist they have jurisdiction.
The third is likely if there's a way to pass as both. It's probable different IDs would be used, though in a less grimdark setting (or just a less grimdark CITY than Brockton), they might get away with being open about the dual-membership. If they give away that identifying info, again.
The reason for the third option would be a combination of "useful and needs the money" with "superiors care about the kid's socialization and want to make sure he hangs out with people his own age as well as adults."
The third option would likely take the form of doing all his duties as a Protectorate hero, but also frequently going on patrol with a Ward in Ward-safe parts of town. Also being encouraged to spend time - free and official - attending Wards social events. Even if it's just the Wards getting together to do a team-building exercise, he'd probably be pushed into any Protectorate-representative position for it, just to encourage him to spend time with other superpowered kids.
But when the chips are down, he's paid to be a mature adult Protectorate hero, so he gets called on for the same stuff other Protectorate heroes are. And he's expected to live up to Protectorate standards of paperwork, ethics, etc., getting away with none of the shenanigans that Wards can play the "he's a kid; just scold him" card to survive.
and will be forever as seniority is a bitch 
is taylor being nice 
