INDIANAPOLIS — Their floor leader is out, and no one knows how long. Their margins are so narrow, no one knows how long their run can last. Their lineup is so young, with three freshman starters, Juwan Howard couldn’t help but reminisce. “If I remember, Coach (Steve) Fisher started five freshmen,” Howard said with a laugh, recalling his Fab Five days. “Some people would say, it’s a very young team. True, it is. But did they grow up today? Yes.” The Wolverines had to grow up quickly in their NCAA Tournament opener, and when the critical moment came — respond or recoil — freshman Frankie Collins…