Twenty Years Old
noun
Two times ten years old is twenty years old.
Since 〜歳 can be replaced with 〜才, 二十歳 can also be written 二十才. Either way, it still means you're officially an adult in Japan… even if you don't feel like one yet.
The reading for twenty years old, specifically, is a really weird reading. It's はたち. When you turn twenty years old you become a hater of cheese. A hater cheese (はたち) kinda person.
「僕は二十歳になる前に社長になるよ。」「そうだといいけどね。」
"I’ll be company president before I’m twenty years old." "I hope you’re right about that."