Don't tell them your age, then. Age discrimination is illegal so they can't ask how old you are and you don't have to tell them.

I was contacted by a well-known men's magazine when I was in my teens regarding some blog/Usenet posts I'd written. They wanted me to go to a conference in the US and cover a story for them. The initial e-mail thread went very well then I made the mistake of admitting I was 16 on the first call and never heard back from them.

Covering a conference they'd eventually have figured it out - but with dev work the client need never know your age and as long as you are legal to work, they need never know.