Definitely - had a 5 year old run a GRHRCH in Started and that young lady went home with a ribbon. That is one of the great things about HRC, it encourages the youth to participate so they will be the hunters and members of tomorrow.
You can also do the same thing in AKC hunt tests, any handler under 18 years of age can run any titled dog at any level. So a young person could run a MH in Junior. Great way to give them some line experience!