Past one's peak in more ways than one (4,3,4)
I believe the answer is:
over the hill
Here is my best explanation:
'peak in more ways than one' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'past one's' is the subsidiary indication.
I cannot quite see how this works, but
'past' could be 'over' (I've seen this in other clues) and 'over' is present in the answer.
'one's' could be 'i' (I've seen this in other clues) and 'i' is present in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for over the hill that I've seen before include "as 20 [OLD MAID]", "Duke of York's men didn't get this far", "walk up and down here?", "Getting on", "past one's prime", "Obscured by the scenery", "Up and down", "Into the next valley", "generally declining" and "Past one's best".)