It is freely available and defined in RFC 2144. http://www.faqs.org/rfcs/rfc2144
... city the population is spread out with 27.2% under the age of 18, 8.7% from 18 to 24, 29.5% from 25 to 44, 21.0% from 45 to 64, and 13.5% who are 65 years of ag ...