Twenty Years Old
Two time ten years old is twenty years old.
はたち
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."