Old man in poems (4)
I believe the answer is:
odes
'poems' is the definition.
(ode is a kind of poem)
'old man' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'man' becomes 'des' ().
'o'+'des'='ODES'
'in' acts as a link.
(Other definitions for odes that I've seen before include "Songs" , "Lines" , "Poets write them" , "Verses" , "poetry" .)