Older boy was about 3 1/4 yrs when the younger boy (@ about 5-6 mths) started sharing the room next to us. Most of the time it works unless DS2 is sleeping and we want to put DS1 in time out. Currently they're about 3 3/4 yrs & 13mths. DS1 doesn't wake to DS2s night feeds / crying unless he's managed to wet his bed around the same time (joys of night training) thankfully that's only usually around 5am