A way to grow old in the theatre (5)
I believe the answer is:
stage
'the theatre' is the definition.
(stage is a kind of theatre)
'a way to grow old' is the wordplay.
'a way' becomes 'st' (abbreviation for street).
'to grow old' becomes 'age' ('age' can be a synonym of 'grow old').
'st'+'age'='STAGE'
'in' acts as a link.
(Other definitions for stage that I've seen before include "Acting area" , "Phase; mount" , "period" , "Elevated platform" , "Theatre platform; leg" .)