The "ii" is likely a typo.
Here are some examples of how "à quel âge" is used in a sentence:
* À quel âge as-tu appris à lire ? (At what age did you learn to read?)
* À quel âge est-il parti à l'école ? (At what age did he go to school?)
* À quel âge as-tu eu ton premier enfant ? (At what age did you have your first child?)