The most common and most likely answer to this crossword clue is the 9 letter word STRIPLING
I've seen this crossword clue in The Times
S
T
R
I
P
L
I
N
G
More clues leading to the result STRIPLING
- Youngster, small, getting much bigger
- Youth shy to admit blunder
- Drug-taking experience embraced by shy youth
- Youth in cast concealing slip
- Boy band with endless patter
- Young lad taking alcoholic drink, about to stumble
- Journey embraced by supporter, young man
- Juvenile error loading old weapon
- Lad with catapult taking tumble
- Second journey made by Heather as a youngster
Buddy explains!

The straight part
We know that "youth" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case youth = stripling.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 STRIPLING mean?
STRIPLING noun- (sometimes humorous) A youth in the state of adolescence, or just passing from boyhood to manhood; a lad. .
- A seedling with most of the leaves stripped off.