Obvious ambassador fell, being elderly? (4,3,4)
I believe the answer is:
over the hill
'elderly?' is the definition.
(thesaurus)
'obvious ambassador fell' is the wordplay.
'obvious' becomes 'overt' (similar in meaning).
'ambassador' becomes 'HE' (His or Her Excellency).
'fell' becomes 'hill' (I've seen this before).
'overt'+'he'+'hill'='OVER-THE-HILL'
'being' acts as a link.
(Other definitions for over the hill that I've seen before include "Duke of York's men didn't get this far" , "walk up and down here?" , "Obscured by the scenery" , "generally declining" , "past one's prime" .)