From what I've read, there is a *tendency* for kids who are early virtually across the board to be GT. But that does NOT mean that kids who are not early at everything will be not-GT. (If that makes sense...)
More than anything, I think parents who suspect GTness (and are being really honest with themselves) are usually correct, so if you are using a critical eye and still suspect GTness in your youngest, you're probably right.
FWIW, I had my first inklings of GTness in my older son when he was about that same age--8mos. He used logic to reason out the boundaries of a rule before he could walk or really speak more than a word or two, and then he followed the rule. I was pretty sure that was unusual... So it is certainly possible to see some early evidence.
