Crossword Genius

Intellectual ability, important issue for older people? (4,6)

Ross

I believe the answer is:

grey matter

I'm a little stuck... Click here to teach me more about this clue!

'intellectual ability important' is the definition.
I can't tell whether this defines the answer.

'issue for older people?' is the wordplay.
'issue' becomes 'matter' (synonyms).
'for' means one lot of letters go next to another (I've seen this in other clues).
'older people?' becomes 'grey' (I can't explain this - if you can you should believe this answer much more).
'matter' after 'grey' is 'GREY MATTER'.

Can you help me to learn more?

(Other definitions for grey matter that I've seen before include "Intelligence; the brain" , "intellectual capacity?" , "Issue lacking clear boundaries" , "stuff in the head" , "Brains" .)

I've seen this clue in The Times.
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