Bouncing in might try those of a certain age (15)
I believe the answer is:
thirtysomething
'of a certain age' is the definition.
'bouncing in might try those' is the wordplay.
'bouncing' indicates anagramming the letters.
'in'+'might'+'try'+'those'='inmighttrythose'
'inmighttrythose' anagrammed gives 'THIRTYSOMETHING'.
(Other definitions for thirtysomething that I've seen before include "Bridget Jones, say" , "Approaching middle age" .)