Cryptic crossword clue
Checked out old soldier’s unruly youth 6

The most common and most likely answer to this crossword clue is the 6 letter word VETTED

I've seen this crossword clue in The Daily Telegraph
V
E
T
T
E
D

Buddy explains!

The straight part
We know that "Checked out" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case checked out = vetted.
The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.
This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.

What does VETTED mean?

VETTED verb
  1. To thoroughly check or investigate particularly with regard to providing formal approval.
VETTED adjective
  1. Having undergone an investigation and been approved.

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