That's one good solution. Okay we're getting closer to solving the problem of Masters racing. So to the original poster who is a new 55 year old racer, and asking which field to enter, we'd say, "Race in the only field you're eligible for, the Cat 5's". Based on my experience in WA State and more locally in Spokane, this might be a hard sell. But I'm going to talk to some of the WSBA people and see what they think about that change.
As a 37 year old who's both slow for my age AND my category, I really consider myself a neutral party in the discussion. But as an official and a race promoter I just want to make the sport as accessible as possible for everyone.