My fairly average daughter hit almost every milestone early. My twice exceptional son was late at everything except walking. Neither crawled.

I assumed my daughter was very bright because of her early skill acquisition. But in about 4th or 5th grade her peers began to catch up and now she is only in the top 25% of her class. Her IQ scores range from average to high average.

Milestones can be an indication of giftedness, but it is not a slam dunk.