I just put about 20 rides on my 2 yr old APHA gelding this fall. (He was 2 1/2 yrs at the time.) During our rides we did walk, jog, trot, canter, forehand pivots, hindquarter pivots, sidepassing, backing, stopping, steering, and even started on some lateral work. We went out on trail rides in the woods. We rode down the road with cars & trucks whizzing by. We rode out alone through the fields down to the pond. I even took him to a show for the walk-trot classes and we ended up placing. I don't feel I pushed him too fast or too hard. All of these events took place over the course of 5 months & I never rode him more than 2x a week or longer than 1 hr. At a time.
I think the more you can expose your horse to during the initial starting under saddle process, the better the horse will be. If you take it slow and avoid progressing, the horse seems to regress. I've started horses both ways & I much prefer the results I get when I treat the young horse as I would expect him to be if he were a trained horse.
Perfect Jin N Scotch - 2004 APHA Palomino Overo Gelding - Western Pleasure and Showmanship
Hanks Rainy Sky - 1998 Black and White Tobiano Paint Gelding - relaxing rides and blazing trails