Your little brother learns how to argue by watching how you argue. Fight fair.

Arguing is a skill, and children pick up whichever version gets modelled in front of them. If disagreements in your house involve raised voices, old grievances and winning at any cost, that is the template somebody younger is carrying into every friendship they will have. You are teaching it whether or not you mean to. Fighting fair in front of them is a strange sort of gift.

In your next argument at home, stick to the thing itself and leave the history out. Let the other person finish, even when you are right. Say when you have gone too far, where your brother can hear it.