I know the title is horrible, but it was the only thing I can think of at the moment. This is a sub-index for Aging Tropes
An index for characters who act, looks, thinks or is in a position different than what is expected for their chronological/biological age. This also includes behavior patterns that don't match their age.
A direct subtrope of Competence Zone
. See also Aging Tropes
Acting or looking older than you appear/are
Acting or looking younger than you appear/are
Having a position that doesn't match your age