Would my son be old enough to play the boon?

My son is in 6th grade and plays the alto saxophone, piano, and trumpet. He wants to play the boon and cello too. His school would lend him a boon to use so it wouldn't cost any money and would probably not be one that is unplayable. My problem lies in the fact that he might not be big enough to play it. He would be 13 when he starts that boon. Is that old enough to play the boon.