I have two kids, twins now 17yo. They just finished their junior year in high school, and actually perform similarly (high) in terms of grades and test scores. But they are and always have been quite different, and it was one of them that drove me to the internet for information.

1. from babyhood, for sure, but I wouldn't say birth
2. With twins we had the control experiment. DH and I worried we were neglecting DT2 while feeding DT1's voracious appetite for language learning before age 2. So we made a conscious effort to help him learn too and he made it abundantly clear he had no interest, which is presumably closer to the norm. DT1 was reading by age 2 yo and reading fluently by age 2.5, and is still a standout in high school classes related to language.
3. For us, the harder question was "what do our kids need academically to thrive?" We made a conscious choice to keep our kids in the neighborhood public schools with only subject acceleration (as available) and to augment where needed. There were some rough spots and hard choices along the way, but we have no regrets. They'll be applying (mostly out of state) to college in the fall, and they are very well-prepared and super-excited about their futures.