tween-age
/ˈtwiːneɪdʒ/(also tween age, 'tween-age, tweenage) informal (chiefly North American )
noun
A person who is nearly, or has only just become, a teenager. Also (with the): such people as a class. Compare tween. Now rare.
adjective
Of, relating to, or intended for tweenagers.
Origin
1930s; earliest use found in The Sun. Alteration of teenage after 'tween.