I finally found it. The rule change is not in the 2008 Masters rulebook, but it is in the Fall newsletter for masters. The new rule states that racers with student or competitor's licenses can race at Masters events, but not at the regional or national championships.http://www.ussa.org/magnoliaPublic/d...NL%2011-07.pdf
Here is an excerpt:
The following is the actual verbiage of our new rule:
1. Alpine Competitor membership holders 18 years and older may race
in Alpine Masters races.
2. Alpine Student membership holders 18–22 years old may race in
Alpine Masters races.
3. Only Alpine Masters members 21 and older are eligible for Alpine
Masters Regional and National Championships.