Something pointed out a few times that I felt bears repeating is, when you are on a well bred horse, Training can be very easy. What holds back the “average amateur” (if there even is one!) is often they are buying horses coming off of other careers - it takes time to unlearn their former discipline’s training, and then time to train them how to event. From their perspective, having a horse going Training at five can seem impossible.
When you have a horse you back yourself, it’s very different. Those horses come out of the gate on much better footing than a horse coming off the track or from another discipline. Some of them already have the natural balance and confidence in their body that you[g] would spend months installing on an off-track horse.
My last horse that went Training did so at 6 - ironic to the topic of this thread, I took him back down to Novice shortly after. He had the scope that made any Training question incredibly easy, but his rideability wasn’t there and frankly, my riding wasn’t as good either. I joined a BNT program to work specifically on this. Most of the horses in this BNT barn were four to six years old and going Training or Prelim. He was considered “behind” in his education. When you are in a top class barn, with young horses going through the “UL Pipeline”, you’ll realize that for them, Training is not a big ask at all.