One entertaining the mature trifle? Wow! (3,3)
I believe the answer is:
toy boy
'one entertaining the mature' is the definition.
I know nothing about this answer so I can't judge whether this works.
'trifle? wow' is the wordplay.
'trifle?' becomes 'toy' (I've seen this in another clue).
'wow' becomes 'boy' (I can't justify this - if you can you should give a lot more credence to this answer).
'toy'+'boy'='TOY BOY'
Can you help me to learn more?
(Other definitions for toy boy that I've seen before include "Woman's young lover" , "Much younger male lover of older woman" , "Older woman's fancy" , "Young male lover of older woman" , "Gigolo" .)