Your friends are people you know well and like spending time with. You can refer to a friend who you know very well as a good friend or a close friend.
He's a good friend of mine.
A close friend told me about it.
If someone has been your friend for a long time, you can refer to them as an old friend. He or she is not necessarily an old person.
I went back to my hometown and visited some old friends.
‘be friends with’
If someone is your friend, you can say that you are friends with them.
You used to be good friends with him, didn't you?
I also became friends with Melanie.