noun
how old; what age
Used to ask someone's age. Polite when combined with ですか or おいくつですか, but 何歳 can be direct; use おいくつ for extra politeness.
あなたは何歳ですか。
How old are you?
この子は何歳になりましたか。
How old has this child turned?
Compound of 何 (なん, 'what') and 歳 (さい, counter for age). The alternative spelling 何才 uses a common substitute character for 歳.