For my classes, I request that dogs already have a minimum of Basic obedience training for my Rally classes. What I consider Basic: sit; sit & stay; lie down; down & stay; heel on-leash; come when called; ect. All Novice Rally exercises are performed on-leash.
However, about 90% of my Rally students are prior clients who've already taken their dogs through my Basic; Intermediate; and Canine Good Citizen courses.
The only age restrictive advice I'd give (especially for large dogs) is don't try Advanced or Excellent Rally exercises until they're mature since these include exercises with jumps. Advanced & Excellent Rally exercises are performed off-leash.
