They are happy to see you!
They handle stress and disappointment well.
They don’t externalize their frustrations, and take responsibility for solving their own problems. They act like a functioning adult.
They have interests and hobbies that they are happy to do alone, or share.
Unfair - but they don’t have intense money, drug, social pressure in their life, a stable situation is the good grounds for relationships
bonus: If their parents are attractive, then they could be a good partner who ages gracefully with you
That bonus really looked like it was going somewhere else for a second there.