When I first started racing I did the Cat 5 race at Cherry Pie. Nate English, who ran track at Cal, was in that race, rode off the front and lapped the field. I think it may have been his first or second race ever. By the end of the season, he was a Cat 1. The season after that, he signed a pro contract. I was still a Cat 5.
So, yeah. It can happen.