Yeah, I just mean that their body wouldn’t be developed enough to be that coordinated or strong. Even bringing magic/ki into it, I feel it bends suspension of disbelief. They’re also being treated like they’re much older than they are by the Sect members who have no idea they’re an adult in a child’s body.
EDIT: I do want to be clear though, it would totally work fine if the MC was just a little older. You wouldn’t even need to edit much.