Record old companion's age (5)
I believe the answer is:
epoch
'age' is the definition.
(both can mean a period of time)
'record old companion's' is the wordplay.
'record' becomes 'EP' (abbreviation for extended play record).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'companion' becomes 'ch' (Companion of Honour).
'ep'+'o'+'ch'='EPOCH'
(Other definitions for epoch that I've seen before include "Long period of time" , "remarkable time" , "Period, era" , "Aeon" , "years" .)