One scheming young wizard, about fifty (7)

I believe the answer is:

plotter

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'one scheming young' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.

'wizard about fifty' is the wordplay.
'wizard' becomes 'potter' (Harry Potter).
'about' indicates putting letters inside.
'fifty' becomes 'l' (Roman numeral).
'potter' placed around 'l' is 'PLOTTER'.

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(Other definitions for plotter that I've seen before include "Schemer" , "One who schemes" , "Conspirator" , "Conspirator's" .)

I've seen this clue in The Times.

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