2012 USAC Rulebook
(excerpt)
1A30. A rider's racing age shall be his age on December 31 of the
current year except in cyclo-cross.
A rider's racing age in cyclo-cross is his age on December 31st
of the year that the cyclo-cross season ends.
References to age of riders, race age groups, or age class shall
be interpreted as referring to racing age. The following terms
refer to specific age groups.
USAC Racing Age / Group Class
6-9 Youth
10-18 Junior
19-22 Under 23
23-29 Elite (i.e. senior)
30+ Master
- - - -
Note: September 1, 2012 - Feb 28, 2013, is the UCI CX season.
UCI CX classes differ.