My oldest (6th grader) was in GT during 4th and 5th. We decided not to continue with GT since our local middle school is amazing and GT middle school is far and inconvenient. He was not especially quick to learn walking: at 13 months maybe... Has big motor skills always were very good (For instance, he moves very gracefully. Oddly he has no talent for sprinting - he does not change the lengths of his strides - from short and quick to long - as a his speed increases. This is very odd to me since it seems so intuitive). At some early pediatric visit we were asked: "does he know 50 words?" We were not sure. They seemed worried about that and I guess so were we as a result. He had one ear infection after another and that might have contributed... Then at the next visit they asked something like does he know a few hundred words and we thought that he pretty much had a vocabulary in the thousands. So everybody has their own schedule. Now he's in 6th grade an his Lexile range is 1526-1676 and his RIT score was 257 (BTW should we be worried that this is the exact same score he had last last year in 5th grade?)
Our second boy was extreme in that he spoke in sentences at age 9 months (comprising an object and a verb such as "I don't want to" and "I'm hungry"). But of course it was not always grammatically correct and often words were pulled together (I.e "I don't want to" sounded like "I nanto.") Still very early, I guess. He is clearly very smart (maybe smarter than his older brother but has not distinguished himself in school yet. He seems very relaxed about it and not as driven as his older brother). We'll see what happens.