The text does not say for certain. Certainly Ophelia is treated like a child whereas Laertes is treated like someone more mature, but this may not be a true indication of their respective ages. Polonius and Laertes (and Hamlet for that matter) treat Ophelia as if she has no mind of her own, no capability of acting on her own. And indeed this appears to be the case, but it may be because she has always been treated like that, not because she is young.
It illustrates Laertes close relationship to Ophelia.
Laertes instructs Ophelia to stay away from Hamlet because he believes that Hamlet will not be able to marry Ophelia even if he really does love her.
to get a life
Polonius, Ophelia, Gertrude, Hamlet, Claudius, and Laertes.
Which of Laertes' actions are we talking about? His leaping into Ophelia's grave? His statement that in terms of honour he remains aloof? His stabbing Hamlet with an unbated sword?
It illustrates Laertes close relationship to Ophelia.
Laertes is the son of Polonius and the brother of Ophelia.
Laertes instructs Ophelia to stay away from Hamlet because he believes that Hamlet will not be able to marry Ophelia even if he really does love her.
to get a life
In Ophelia's grave.
Both Laertes and Hamlet.
Laertes jumps into the grave
Polonius, Ophelia, Gertrude, Hamlet, Claudius, and Laertes.
Ophelia is the daughter of Polonius (the king's main advisor), the sister of Laertes, and the beloved of Hamlet.
She tells him that Ophelia has drowned.
That character Ophelia is a central person in the Shakespeare classic Hamlet. Potentially married to Hamlet, Ophelia is the sister of Laertes who kills Hamlet.
He says as much. "I loved Ophelia! Forty thousand brothers with all their quantity of love could not make up my sum." Of course, whether he really believes it or is trying to make fun of Laertes' pomposity is another matter.