Most tractor shows that I have gone to prefer 25+, but other factors at a show are not only age but uniqueness, rarity, condition, out of production, manufacturer still operating, unusual features, how long owned, etc. Your tractor would bring more interest than a much older but very common John Deere or Farmall.
I've had people chase me past rows of beautiful old Deere's to learn what my little tractor was and all about it!
You have as much right to be proud and show your tractor as anyone else.
It is also easier to preserve it than to restore it!!