It's originally a way to refer to a young person, but can now also be used as a way to refer to someone of the same age or older if you have enough confidence with that person.
"¡Epale chamo! ¿Cómo estás?" |
"¿Puedo invitar a tu hermano a la fiesta?"
"No puede ir, está muy chamo aún."
"Hey dude! How are you?" |
"May I invite your brother to the party?"
"He cannot go, he's still too young."