age out

age out
 v. phr.— «Amy Weldon is what’s called a rook-out, a first-year rookie who’s aging out of the corps. She says her first—and last year—has offered her memories that will last a lifetime.» —“Drum Corps Groups March Out of Madison After Championships” by Dana Brueck WMTV-TV (Madison, Wisconsin) Aug. 12, 2006. (source: Double-Tongued Dictionary)