Stating Age with อายุ and ขวบ or ปี

Thai normally states age with อายุ + number + ปี/ขวบ: อายุยี่สิบเอ็ดปี “be twenty-one years old.” There is no equivalent of inflected English “am/is/are” inside this frame. อายุ supplies the relation “age,” the cardinal gives the completed count, and ปี or ขวบ names the unit.

ปี is the general unit and works for people of every age, especially in neutral and formal contexts. ขวบ is child-oriented: the Royal Society defines its age use for children of roughly twelve and under. Adults may jokingly use ขวบ about themselves (playful informal), but that is a marked effect, not the neutral alternative to ปี.

The basic อายุ frame

Put the person or topic first when it needs to be stated, then อายุ, the complete cardinal, and the age unit. Thai does not require a subject pronoun when the person is already clear.

The final one in ยี่สิบเอ็ด follows the normal careful cardinal rule explained on the final-one page. ปี does not cause เอ็ด; the number itself ends in 1. Thai verbs and predicates do not agree with the person or change form for age.

ปี: the general and formal choice

Use ปี with adults, with statistical ages, and whenever the register is neutral or (formal). It is also fully correct for children. Forms and eligibility rules often use อายุ...ปี because ปี is an ordinary time unit that supports exact administrative measurement.

In ผู้สมัครอายุสิบแปดปี, ผู้สมัคร is the person whose age is measured. In เด็กอายุห้าปี, the whole อายุ phrase modifies เด็ก: “a child aged five.” Thai builds this relation as a phrase rather than changing “five” into an adjective like English “five-year-old.”

Here อายุห้าปี describes เด็ก, while สองคน independently counts the two children. Do not attach a person classifier inside the age itself.

ขวบ: the child-oriented unit

ขวบ means a yearly cycle and functions as a conventional age unit for children, approximately age twelve and below. It sounds especially natural when parents, relatives, teachers, or health workers talk about a young child. ปี remains possible; the difference is viewpoint and register, not arithmetic.

Calling a forty-year-old สี่สิบขวบ can be humorous or affectionate (playful informal). Without that intention, use สี่สิบปี.

Asking age and managing social context

The ordinary grammatical question is อายุเท่าไร. Add the person when needed: ลูกอายุเท่าไร “How old is your child?” Because an adult’s age can be personal, grammatical correctness does not guarantee social appropriateness. In service or medical settings, explaining why the information is needed makes the question more considerate.

The reply does not repeat ลูกสาว or อายุ. Thai permits zero anaphora because the question keeps both recoverable.

ครบ, เต็ม, and ย่างเข้า

An unmodified age such as อายุห้าปี conventionally reports completed age: five birthdays have passed. Three extra expressions sharpen the boundary.

• ครบห้าปี / ครบห้าขวบ means “reach five years,” focusing on the fifth anniversary or eligibility threshold.
• ห้าปีเต็ม / ห้าขวบเต็ม means “a full five years,” emphasizing that the count is fully completed. It is common in (formal) admission and benefit rules.
• ย่างเข้าปีที่หก literally means “enter the sixth year”: five years have been completed and the sixth year of life has begun. In casual speech, people sometimes use ย่าง loosely for “approaching,” so official rules must be read according to their stated definition.

Do not equate ย่างเข้าปีที่หก with the completed age หกปี. If exact eligibility matters, a birth date or the phrase ครบ...ปีบริบูรณ์ is clearer than casual ย่าง.

Common Mistakes

1. Copying English “be” with เป็น

2. Putting the unit before the number

3. Using ขวบ neutrally for an adult

4. Reading 21 with หนึ่ง at the end

5. Confusing a year entered with completed age

Key Takeaways

Use อายุ + cardinal + ปี/ขวบ without เป็น. ปี is general and formal; ขวบ frames someone as a child, conventionally around twelve or under. Bare ages report completed years, ครบ and เต็ม make a threshold explicit, and ย่างเข้า names the year of life being entered. Thai relies on phrase structure, number formation, and discourse omission rather than English copulas or adjective inflection.