Why is that? Is there a rule stating that people under the age of 21 (or 18 as it is in my country) are unable to find out more about their health on this site? Seems a bit closeminded to me. But just curious so I can know if I'm actually allowed to post "why do some cheeses give me stomach upset and not others" or other things i'm wondering, or if i'm banned for another 6 months from questioning on account of my minor status.
(I've even tried looking on the FAQ but got a 404 message)
there is some info under the 'Terms of Service' for the site, here's the relevant text;
Collecting personal information from children under the age of 18 ("minor children") through the Services or PaleoHacks.com is prohibited. No Content should be directed toward minor children. Minor children are not eligible to use the site, and we ask that they do not submit any personal information to us.
(and the site FAQ can be found here)
It's in the Terms of Service which you were required to read/accept when you joined PH so this shouldn't be a surprise. Because we are not doctors, and you are not paying us as a professionals. If somehow the advice turns out to be wrong, or potentially harmful, as it can be, you could be putting yourself at a health risk based on our advice, and your parents/legal guardian could sue for our suggestions to you. So it is just for legal liability.
Besides , none of us have the authority to change this, you would need to contact the site owner to petition a change.