Hey there Smelly as Invoked by Red he is partially right, I will say this thought, the age for the betas are not the same as the age for the forum follow this link: connect.microsoft.com/.../content.aspx
It clearly states this in case you can not go to the link :Q: Is there an age requirement for participation in the Microsoft Game Studios Beta Program?
A: Yes. If you live outside of the United States, you must be at least 18 years old to register in Connect. U.S. residents must be at least 16 years old to register. If you are a resident of the United States with a valid United States address, and you are
between the ages of 16 and 18, you will need to complete a Parental Consent Form (valid only in the United States) prior to registration.
I can't quite remember the terms exactly. But you have to be at least thirteen to post on these forums. So if you don't meet the minimum requirement for these forums, it's safe to assume you can't sign up to the beta.