My 2 oldest DSs co-slept with each other from about 5 & 3 years old. DS1 slept with me until he was 2 then started in his own bed and migrated most nights. DS2 never slept with me as a baby and would only come in if he was sick or scared. When DS2 was about 3 I think he just decided he'd like to sleep with his brother and did so until he was about 8 or 9 even I think