It is freely available and defined in RFC 2144. http://www.faqs.org/rfcs/rfc2144
... with 22.3% under the age of 18, 8.0% from 18 to 24, 31.0% from 25 to 44, 21.9% from 45 to 64, and 16.9% who are 65 years of age or older. The median age is 39 years. For ...