A famous competitive programming prodigy is tourist[1]. You can find his rating graph starting from 2006 on topcoder when he was just 12 years old: https://www.topcoder.com/members/tourist/details/?track=DATA...
He's now indisputably the best competitive programmer in the world. But it's comforting to know that he too had to slowly grow over many years starting from a mere mortal 1200 rating.