Is he really ready?

I am way too impressionable sometimes and I doubt my decisions too easily. This is no body's fault but my own and something I struggle with daily. Today's self doubt. My five year old being ready for kindergarten. I'm not ready for this big step just because it means my baby boy is growing up too fast. He on the other hand is totally excited and says he's ready. And he really is smart. He knows his ABC's, can count pretty far, knows his shapes and colors. He's inquisitive about everything and retains information amazingly well. He's constantly telling me random facts about animals and things. He's wonderful at teaching his three year old sister. He's sweet and compassionate. Has an extensive vocabulary and honestly understands the words he's using. The only points that concern me are that I never really let him on the computer, he's very sensitive and cries easily, and he still has issues with sharing. Although the last is mostly just with his siblings. He does pretty well when friends come over to play. My daughter Jordyn didn't start until she was six but that was in another state. Where can you reliably research the standards for the state you live in? When do you stop researching?  How do you know when your child is ready for something? And how much information do you listen to from others? When is the right time to believe in your own judgement?