Our situation is a little different, as we adopted my son as an infant. He is only 3 months younger than our bio son. Currently they are only 2 1/2, but they will most likely start school the same year (making them in the same grade). One is CA and one is AA. The boys are very close and you can definitely tell they are brothers when you watch them interact. They are not school age yet, but I can only imagine the questions we/they will get. At this point, I would do it again in a heartbeat.
Good luck with whatever you decide.