How old clothes are rubbish! (7)
I believe the answer is:
garbage
'are? rubbish' is the definition.
'garbage' can be an answer for 'rubbish' (both can mean refuse or trash). I'm not certain of the 'are?' bit.
'how old clothes' is the wordplay.
I cannot really see how this works, but
'clothes' could be 'garb' (garb is a kind of clothes) and 'garb' is found within the answer.
'how old' could be 'age' (I've seen this before) and 'age' is located in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for garbage that I've seen before include "A beggar? - that may be rubbish" , "Refuse - a beggar (anag)" , "Waste, refuse" , "Litter" , "'Refuse, rubbish (7)'" .)