Crossword Genius

Not old enough for a state nurse (3)

Ross

I believe the answer is:

ten

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

'not old enough' is the definition.
The definition and answer can be both quantities as well as being singular nouns.
Maybe there's a link between them I don't understand?

'a state nurse' is the wordplay.
'TEN' is hidden in amongst the letters.
However, I'm uncertain how the hidden word is indicated.

'for' is the link.

Can you help me to learn more?

(Other definitions for ten that I've seen before include "How many" , "Five times two" , "Base of decimal system" , "X-WORD" , "Half a score" .)

I've seen this clue in the Evening Standard.
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