How Old Are You in Japanese? The Natural Age Patterns
The most common way to ask how old are you in Japanese is 何歳ですか (なんさいですか). A more polite version is おいくつですか. To answer, use number + 歳, like 二十五歳です. The biggest beginner trap is 二十歳, which means 20 years old but is read はたち, not a regular number-plus-sai form. This page also shows which version sounds more polite and how to answer naturally in a first-meeting conversation.
Enter an age to make a simple, polite self-introduction dialogue. Notice the special reading for 20 years old: 二十歳(はたち).
Culture note:おいくつですか is polite, but asking an adult stranger their age can still feel personal. Use it when the context makes the question relevant, or let the other person volunteer the information. Avoid the more direct 何歳ですか with customers or older adults.