quel âge as-tu (quite correct)
quel âge tu as (not grammatically perfect but much more in use)
take a french class or write it down in french or kiss her or he
quel âge avez-vous?
How old are you? = Quel âge avez-vous?
"How old are your twin daughters?" would be translated in French "quel âge ont tes jumelles ?"
ask one of her/his friend or ask one of your friend to ask her/him.
"Quel âge as-tu ?" (if you're talking to a friend) or "Quel âge avez-vous ?" (polite form).
Vieil ami
you ask him.
Quel age as tu?
ask her out
i don't know why don't you ask a french person
listen, you're not old enough for boyfriends yet,Ok? I'm 10 too OK? Leave it for a few years then ask him out!! Your friend might be too mature by then to butt in.