The most common and most likely answer to this crossword clue is the 6 letter word CALLOW
I've seen this crossword clue in The Guardian
C
A
L
L
O
W
More clues leading to the result CALLOW
- Ring round with Green
- Immature depiction of everyone in Jersey, say?
- Animal that’s swallowed completely raw
- Naive actor having to visit town- centre
- Jersey, say, worn by everyone is green
- Contact that hurts juvenile
- Muncher of grass munching everything green
- Immature animal eats everything
- Too inexperienced to express pain
- Too inexperienced to express pain?
Buddy explains!

The straight part
We know that "Immature" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case immature = callow.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 CALLOW mean?
CALLOW noun- A callow young bird.
- A callow or teneral phase of an insect or other arthropod, typically shortly after ecdysis, while the skin still is hardening, the colours have not yet become stable, and as a rule, before the animal is able to move effectively.
- An alluvial flat.
- Unfledged (of a young bird).
- (by extension) Immature, lacking in life experience.
- Lacking color or firmness (of some kinds of insects or other arthropods, such as spiders, just after ecdysis); teneral.
- Shallow or weak-willed.
- (of a brick) Unburnt.
- Of land: low-lying and liable to be submerged.
- Bald.