Young
Used informally for 'boy' or 'girl', often implying a teenager or young adult. Very common in casual conversation.
Similar to 'chico/chica', meaning 'young man' or 'young woman'. Slightly more traditional-sounding in some regions.
Literally means 'small' or 'little', but is used to describe young children. You'd say this about your son, but not a 20-year-old.
My brother is young. He is 20 years old.
The students in the class are very young.
She is a very intelligent young woman/girl.
My son is still too young to go to school.
The word 'joven' is universal and understood everywhere. The main variations are in informal slang.
It's very common to use 'chavo' (for a young man) or 'chava' (for a young woman) in casual conversation.
You will frequently hear 'pibe' (for a boy/young man) and 'piba' (for a girl/young woman).
The word 'pelado' or 'pelada' is common slang for a teenager or young person.
Informally, 'cabro' and 'cabra' are used to refer to young people or 'guys' and 'gals'.
The slang equivalent is 'chaval' (male) or 'chavala' (female). The standard word 'joven' is also perfectly common.
Saying 'Mi hermana es jovena.' — The adjective 'joven' is special. It does not change for gender. It's 'el hombre joven' (the young man) and 'la mujer joven' (the young woman). The correct sentence is 'Mi hermana es joven.'
Using 'joven' for objects. — 'Joven' is only for people or living things. For an object, like a car, you should use 'nuevo' (new). Incorrect: 'Mi carro es joven.' Correct: 'Mi carro es nuevo.'
Using 'joven' for a baby. — 'Joven' implies a teenager or young adult. For a baby, use 'bebé' or 'pequeño'. Incorrect: 'El bebé es joven.' Correct: 'El bebé es pequeño.' (The baby is little/young).