My dd will be 4 this June and we will be sending her to school next year.
However, my ds who is a June baby as well, will most likely not go until he is 5.
It totally depends on your child. My dd would be bored if she were to stay home another year, and socially she will thrive. My ds on the other hand, already doesn't have the language skills my dd had at his age or social/emotional, or reasoning skills. He will be much more benefited by having the extra year out of formal schooling.