Harry Potter was 11 years old when he got his Hogwarts letter in "Harry Potter and the Sorcerer's Stone," and that just so happens to be the exact age Daniel Radcliffe was when he started playing the role. Radcliffe started acting at an incredibly young age, and his performance in a 1999 "David Copperfield" miniseries caught the attention of "Sorcerer's Stone" director Chris Columbus.

Columbus quickly cast 11-year-old Radcliffe as the movie's lead, but he wasn't even the youngest actor in the cast. Emma Watson first played Hermione Granger when she was just 10 years old, and 12-year-old Rupert Grint rounded out the main trio as Ron Weasley. All three actors spent a huge chunk of their formative years on the set of the "Harry Potter" movies. Filming the entire series took 10 years, and Radcliffe was 21 on the emotional last day of filming when the crew shot the ending of "Harry Potter and the Deathly Hallows — Part 2."

Plenty of famous Hollywood stars started as child actors, but few of them were as famous as Radcliffe. "Harry Potter" was an unprecedented worldwide sensation, and starring in the series changed Radcliffe's life forever. Years after the end of the series, Radcliffe has plenty of thoughts about his childhood stardom and a serious piece of advice for the people making the "Harry Potter" reboot series.