Kid who takes seven years to make a score (4)

I believe the answer is:

teen

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'score' is the definition.
Both the answer and definition are adjectives. Perhaps they are linked in a way I don't understand?

I cannot understand how the remainder of the clue works.

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(Other definitions for teen that I've seen before include "Young person" , "Juvenile" , "Youngster over twelve" , "Youngster of a certain age" , "Of 13 to 19 year olds" .)

I've seen this clue in The Irish Times.

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