Division in band that's getting older (7,2)
I believe the answer is:
growing up
'getting older' is the definition.
Although both the answer and definition are present participle verbs, I can't see how they can define each other.
'division in band' is the wordplay.
'division' becomes 'wing' (I can't justify this - if you can you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
'band' becomes 'group' (I've seen this in another clue).
'wing' put within 'group' is 'GROWING UP'.
'that's' is the link.
Can you help me to learn more?
(Other definitions for growing up that I've seen before include "getting bigger?" , "showing more mature attitude" .)