listen to the pronunciation of callow
Englisch - Englisch
Lacking color (of some newly emerged adult insects)
Shallow or weak-willed
Unfledged (of a young bird)
Unburnt (of a brick)
Immature, lacking in life experience

Those three young men are particularly “callow youths”.

without experience of the world
{a} wanting fethers, unfledged, naked
Not having the experience and sophistication expected of an adult, or of one in a responsible position
See Old squaw
A kind of duck
A callow young person has very little experience or knowledge of the way they should behave as an adult. a callow youth. young and without experience - used to show disapproval = immature
lacking experience of life; "a callow youth of seventeen
lacking experience of life; "a callow youth of seventeen"
Bald (original meaning, now obsolete)
{s} without feathers; inexperienced; very young
Immature; boyish; "green"; as, a callow youth
Destitute of feathers; naked; unfledged
The condition of being callow; immaturity
{i} lack of experience; immaturity
lacking and evidencing lack of experience of life