I take dull puzzle and make it seem grown-up (9)

I believe the answer is:

adultlike

I'm a little stuck... Click here to teach me more about this clue!

'make it seem grown-up' is the definition.
I can't judge whether this defines the answer.

'i take dull puzzle' is the wordplay.
'puzzle' is an anagram indicator.
'i'+'take'+'dull'='itakedull'
'itakedull' anagrammed gives 'ADULTLIKE'.

'and' acts as a link.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

Want a hint initially instead of a full solution? Install my app