quel âge as-tu: how old are you?
The question 'Quel age as-tu' asks How old are you. In the word-by-word translation, the interrogative adjective 'quel' means 'what, which'. The noun 'age' means 'age'. The verb 'as' means '[you]...
How old are you
What age are you
Quel âge ("âge" is a masculine noun, "quel" is the masculine pronoun)