Related to the above: I know you mentioned earlier that John hit milestones much more quickly. Don't know if this is similar or not, but my mom thought I was slooooooow. My brother was really, really bright and I just followed along. Mom went to our pediatrician out of concern that something was wrong with me. His response: "She'll do just fine once motormouth lets her get a word in edgewise."
(BTW, I'm smart. Weird, but smart relative to the general population.)