"The earlier you start, the better" is a claim that travels easily through the world of children's extracurricular activities. Piano at three. Swimming from six months. English from the womb. Alongside those claims runs an equally persistent counter-narrative: the child who burned out, grew to hate the thing, and quit.
The question of when to begin does not have a single answer. It depends heavily on which activity is in question and what goal is being pursued. What the research shows is something more nuanced than "earlier is better" or "later is fine."