precocious
Showing advanced skills or talents at a much younger age.
Precocious describes a child who develops certain abilities or shows particular talents much earlier than most other children their age. A precocious six-year-old might read novels meant for teenagers, or a precocious young musician might perform complicated pieces that usually take years more practice to master.
When someone is precocious, they're reaching milestones ahead of schedule: perhaps solving algebra problems in elementary school, or understanding complex ideas that typically come later in life.
People usually use precocious with a mix of admiration and gentle amusement. A precocious child might surprise adults by using sophisticated vocabulary in conversation or showing unusually mature insights. However, being precocious in one area doesn't mean being advanced in everything. A child might be precocious at chess but completely ordinary at sports, or precocious at music but struggle with math.
The word specifically applies to children and young people. You wouldn't call an adult precocious, since they're expected to have developed abilities already. It's a word that captures that special moment when someone young shows a glimpse of the person they're becoming, faster than anyone expected.