A counter for age (years old). Used to indicate a person's or animal's age (e.g., '25 years old').
私は二十五歳です。
I am 25 years old.
子どもは三才で日本語を話し始めた。
The child began speaking Japanese at three years old.
漢字では『歳』、手書きや簡略では『才』を使うことが多い。
The kanji '歳' is standard; the simplified '才' is often used in handwriting or shorthand.
彼女は何歳ですか？
How old is she?