An immature, naïve or inexperienced person.
A young bird which has just developed its flight feathers (notably wings).
An insect that has just fledged, i.e. undergone its final moult to become an adult or imago.
Emergent or rising.
Untried or inexperienced.
A boy or young man.
A groom who works with horses.
A Jack the lad; a boyo.
The penis.
A familiar term of address for a young man.