I would add to that - “when you can consistently string the movements together.” For instance, preparing for a SI with a 10 m circle, and then consistently producing it down the long side is one thing, but it’s another thing to produce the SI out of a corner, and then move quickly to the next movement, and the next. So the transitions and ability for the horse and rider to change and adjust are a big key, and are more and more rapid going up the levels. So maybe a takeaway for someone starting at intro/training, is to remember not to just endlessly school the 20 m circles, but prep to move up by incorporating lots of transitions, changes of direction, etc. even though they aren’t required in the tests yet. Otherwise it can be very discombobulating to learn to manage it later. Just my perspective as a 2nd level rider starting to get my arms around 3rd while training my own horse with minimal coaching.
Examples with my own horses:
Bought 4 year old appendix QH in spring, showed her intro that fall. Fall of 5 yo year she showed a respectable T-3. Sidelined with injury for 18 months, then back to T-3 and 1-1 end of her 7 year old year. At 8 we showed 1st, and then at 9 managed 2-1, though her mediums really weren’t there, and probably needed at least another year to develop, as she just was not built for dressage. However, she was developing a respectable half pass when I sold her at 10.
Started current WB mare at 4. Talented but highly opinionated, so I did not take her anywhere for two years. Fall of her 6 yo year I finally showed Intro. At 7 we did training in the spring and 1st in the fall. This year we started out showing 1-1 and 2-1. Circumstances prevented getting out to other shows, but I’m now prepping to do 2-1 and 2-3 at a schooling show in two weeks. If we can get changes, I expect to be ready for third next summer and she is starting to show glimpses of 4th level work (canter piri). She’s a nice horse, but not naturally talented with the canter, so it is not a linear path with her.