Leaving age was raised to include old lady (8)
I believe the answer is:
emigrant
'leaving age' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'was raised to include old lady' is the wordplay.
'was' becomes 'time' (I can't explain this - if you can you should give a lot more credence to this answer).
'raised' says the letters should be written backwards (going up in a down clue).
'to include' means one lot of letters goes inside another.
'old lady' becomes 'gran' (I've seen this before).
'time' back-to-front is 'emit'.
'emit' enclosing 'gran' is 'EMIGRANT'.
Can you help me to learn more?
(Other definitions for emigrant that I've seen before include "one on the way out?" , "One leaving for another country" , "One going abroad permanently" , "Time Gran went abroad to settle" , "One who leaves to live in another country" .)