Aged around 500,500? (3)
I believe the answer is:
old
'aged' is the definition.
(similar in meaning)
'around 500500?' is the wordplay.
'around' becomes 'o' (I've seen this in other clues).
'500500?' becomes 'ld' (I can't explain this - if you can you should give a lot more credence to this answer).
'o'+'ld'='OLD'
(Other definitions for old that I've seen before include "Long in the tooth" , "Senescent" , "Wild clematis" , "Long-established" , "Obsolete" .)