Being old, agreed about being dropped (4)
I believe the answer is:
aged
'being old' is the definition.
(similar in meaning)
'agreed about being dropped' is the wordplay.
'about' becomes 're' (regarding).
'being dropped' indicates named letters should be taken away (some letters are excluded or dropped).
'agreed' with 're' taken out is 'AGED'.
(Other definitions for aged that I've seen before include "Geriatric" , "Antiquated" , "Matured like wine in wood" , "Advanced in years" , "Old or ancient" .)