Because I, at an early age, was silly (7)

I believe the answer is:
asinine
'silly' is the definition.
(I've seen this in another clue)
'because i at an early age' is the wordplay.
'because' becomes 'as' (I've seen this in other clues).
'at' is a charade indicator (letters next to each other).
'an early age' becomes 'nine' (I can't explain this - if you can you should believe this answer much more).
'as'+'i'+'nine'='ASININE'
'was' acts as a link.
Can you help me to learn more?
(Other definitions for asinine that I've seen before include "Senseless" , "Really silly, ridiculous" , "Is Annie? (Anag)" , "Foolish, silly" , "Jenny's often like this" .)
