The most common and most likely answer to this crossword clue is the 7 letter word GREASER
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More clues leading to the result GREASER
Buddy explains!

The straight part
We know that "Young motorcyclist" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case young motorcyclist = greaser.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 GREASER mean?
GREASER noun- Someone or something that greases (applies grease).
- A mechanic.
- A biker, a tough.
- A rocker or metalhead, especially one who listens to 1950s rock and roll or 1980s thrash metal.
- A Latin American, especially a Mexican.
- An Italian.
- A Greek.