Young forever, lacking regular income, wife must leave (7)
I believe the answer is:
ageless
'young forever' is the definition.
(never aging)
'lacking regular income wife must leave' is the wordplay.
'lacking regular income' becomes 'wageless' (without a wage).
'wife' becomes 'w'.
'must leave' is a deletion indicator.
'wageless' with 'w' taken out is 'AGELESS'.
(Other definitions for ageless that I've seen before include "Not growing older" , "Small amphibian" , "Lasting a long time" , "Eternally young" , "Enduring" .)