Equines are a prey species, so are at their most vunerable when first born. It is most important to be mobile as soon as possible, the foal learns to right itself with seconds of being born. instinctively within 1 hour they can stand and get that important first feed within 2 hours. Young humans have a much longer learning curve and timescale. Standing up on two legs requires tremendous skill that even now machines are only just being able to copy. Yet we don't consciously think to control individual muscles, we just walk, jog or run.
You can imagine that a true centauride born foal would like it's equine counterpart able to stand and move around within hours, although some speculation if the human half would be a youngster of about 5 years old rather than a baby. After all a baby body would lack co-ordination and balance to run away if required.
As an author I get to choose the various parameters of my characters, as a human morphed by magic into a centaur I have to learn how to horse. There are many lucky people who learn to ride from a young age, starting with Pony Club events progressing to larger ponies or horses at a later date. If I intend to write about centaurs, one should at least be able to sit on a horse. Now 58 may be a little old in the tooth, but Smeltings Farm on the outskirts of Sheffield were help to help. The cost of a private yardwork lesson and arena ride was all useful. Sat on a 6 year old Clydesdale mare called, "Margaret," gave me a insight onto how high my centaur draft body would be. Like being sat in an armchair, Margaret was a true gentle giant.
The question my instructor asked was. "what was my purpose of being on horseback?"
I replied. "To have the skill to get a horse to go in the direction I wish to go."
Incorrect.
"Your job as a rider, is to keep her in balance as she moves with your weight on her back."