its 20-29
that's Tolkein's definition of a Tween from the 1930s ... "the irresponsible twenties between childhood and coming of age at thirty-three.
the marketing demographic for Tween is 10-12 ... not a teenager, not a child ... so wanting to BE a teenager but not quite there, but also not just interested in playing (as a child is) ... "too old for toys/too young for boys"