be 100 years too early

slang To be very young, immature, or inexperienced. Commonly used in anime and manga, the phrase is a loan translation (calque) of the Japanese phrase 「百年早い」 (Hyaku-nen hayai). Are you crazy? You're 100 years too early to fight a skilled warrior like him! Please, he's 100 years too early for a management position. He's only two years removed from college! I thought she was 100 years too early for something like this, but her emotional depth and maturity have proven me wrong.