Dr. House wrote:My textbook reads: watashi wa hatachi desu for I'm 20 yo. Is it correct. Why not watashi wa nijuusai desu.
20 years old is special because that's when you become an adult in Japan. Japanese prefers the native Japanese word for this age, especially in the context of 成人式. にじゅっさい is not unheard of though, especially in the news.
Ein Buch muß die Axt sein für das gefrorene Meer in uns. - Kafka