I actually think it's harder for most companies to take a chance on someone remotely when they're so young.
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.
This isn't legal advice, but as someone who worked when I was a teenager, parent consent may be required, so then they'd know you are a minor.
Under US Federal law, it is illegal to work under the age of 14. 14 & 15 can work but only during non-school hours. 16 and older are fine, but under the age of 18, parental consent is required.
Taken from: http://www.dol.gov/dol/topic/youthlabor/agerequirements.htm
The illegal-to-them comes from hiring child labor without the proper consent or regulations met.