I'm sad. My youngest son starts kindergarten tomorrow!
I am sure it is a bittersweet moment.  I can relate myself.  It takes some getting used to
I mean i'm happy for the up coming peace and quiet but it's still sad all my kids aren't babies anymore.
You will still have plenty of time before your son becomes an unruly teenager.  Cherish it.
I've got a 12 year old that's getting mighty close!