How did this happen?

Blake has attended Vacation Bible School every day this week and it is from 9am - 12pm. This seems like a lot for a 4 year old, 3 hours - 5 days in a row, but Blake has done just fine. He walks in, says hello to his teacher, gets his name tag and never looks back. I should be so happy for him and proud that he enjoys himself in a school setting, right? But I am not!! I am sad that he is so grown up :( This is my little Blakey, my first born, how does this happen so quickly??
On the way to drop him off at VBS he said, "Mom I am almost 5 right?" I said not until March 4th. He said, "Yeah, but that is almost here then I can go to kindergarten." Blake has always wanted to grow up, even when he was a baby he tried sitting,standing and walking (at 8.5 months) all too soon. He is always pushing for the next milestone even while I am capturing the current one on camera. He must have sensed my sadness because he said, "Don't worry, Mom, I'll come back after kindergarten." He is so sweet, I am going to love him so much that no woman will ever be good enough for him . .. JUST KIDDING, that is a quote from Monica on "Friends".