Great article! I wholeheartedly embrace it. I took my time starting Walka, training for longevity. Started him at 4, started riding him seriously at 5. Have never regretted it. He's good and solid on the ground and very calm in the saddle. Let his skeletal frame and brain develop without pressure.
Of course, I plan on keeping him till the day he dies, like his mother T, so I was in no hurry to saddle train him.
T was not started under saddle till age 6 and she at age 20 is fit as a fiddle. Never an unsound day (crossed fingers) and hope to have her for many years to come.
When in doubt, always lean to the cautious side. That's my advice.