My 3 year old neighbor has already spent the night at my house. It was more of a sitting thing so mom and dad could go out, but the girls actually did very well together. On the other hand, the neighbor often asks if they can take mine with them and I am nervous and uncomfortable about that whole thing.
I can only tell you, I think 5 is young, but they did just fine at 3 years old.
I know...not much help.