Sam, our Seudos are usually for a Yiddishe cause. We don’t make a Seuda for a birthday, although you might make a party or whatever you want. Avraham Avinu might have been celebrating his special situation.
His coin showed an old couple on side and a young couple on the other. The medrash says that people brought their children to Sara Imeinu to nurse them, just to see and experience the amazing Ness. When Yitzchok was weened that period was completed.