I am past the final stage of development (5)

I believe the answer is:

imago

'the final stage of development' is the definition.
(final development stage of an insect)

'i am past' is the wordplay.
'i am' becomes 'i'm'.
'past' becomes 'ago' (similar in meaning).
'im'+'ago'='IMAGO'

(Other definitions for imago that I've seen before include "Eg monarch finally seen" , "Last state of insect life" , "Final stage of insect life" , "being immature?" , "Beetle, for example" .)

I've seen this clue in The Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.