Past its prime, as the old trumpet is? (9)

I believe the answer is:

overblown

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

'prime as the old trumpet is?' is the definition.
I can't tell whether this definition defines the answer.

'past its' is the wordplay.
'past' becomes 'over' (both can mean finished).
'its' becomes 'blown' (I can't explain this - if you can you should give a lot more credence to this answer).
'over'+'blown'='OVERBLOWN'

Can you help me to learn more?

(Other definitions for overblown that I've seen before include "Exaggerated" , "bombastic" , "pretentious" , "roses being so past their best" , "excessive" .)

I've seen this clue in the Evening Standard.

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.