USA Cycling recently released 2012 changes to the rule book. It appears there aren’t any significant changes that relate to mechanics. Notable changes are the removal of a master category, removal of a tandem championship category and the addition of a youth class. One point of interests is the change in usable bikes for juniors 12 and under:
Young juniors must use mass start legal bikes in all races, including time trials: Beginning in 2012,youth and junior riders in the 12 and under age categories will be restricted to mass start legal bikes in all races. These legal bikes cannot have aero bars. The wheels must have no covers and must have at least 16 spokes. These rules will apply to the 13-14 age group in 2013.
More information to be found on their website via 2012 Rule Changes; 30-34 age group removed from Masters Nationals – USA Cycling.