This is the 219th most frequent Thai word.
ขวบ
"ขวบ" means "year old" (used to indicate age, typically for young children).
The word 'ขวบ' in this sentence is used to indicate the age of a child in full years, specifically used for young children.
ลูกชายของฉันอายุห้าขวบแล้ว
My son is five years old.
In this sentence, 'ขวบ' marks the age of the subject at a specific point in time in their early years of life.
ตอนที่เธอสองขวบ เธอชอบฟังนิทานมาก
When she was two years old, she used to love listening to stories.
Here, 'ขวบ' relates to the typical age of children being described in general observations.