Why did I acquire an independent seat at age 9? 

I had no other choice! 
I was "employed" in the army, at the age 9 and on.   All the riding was free, paid for by the communist state. They would select a small group of kids each year to start.   Then, it was like boot camp: do as you are told. 

It was that, or no riding at all. 

For me, it meant riding 6x a week ... the kids selected for the riding program had to committ to be trained for competition, army style.   Those who didn't fit had to leave.   There was no option to pay for lessons, one had to perform to cavalry standards and keep up good grades in school. 

At age 10, the first 3 months were vaulting only, on vaulting pad. The horse was an Arabian stallion named Ulysses, a fat grey with a wide back and mellow temperament. Very few horses were gelded, and basically only after they had almost killed someone ! 

To "graduate" to saddle and reins, we kids had to pass a test. 
A track was built around the ring and small jumps were set up.   The instructor would ask the horse to go from inside.   Then we walked, demonstrated we can sit or post the trot, canter, jump small jumps -- on the vaulting pad, no stirrups, and our hands had to be up in the air, no holding on.   When we could do that, we were ready to be rewarded by finaly starting to use reins and stirrups.... still had to vault once a week for rider training. 

Today, I want my first time riders to quickly progress to trailrides under my close guidance.   I suppose would have no willing students if I use the way I was taught .... *grin* I prefer my own approach based on learning to communicate with horses early on, and how always slow down / stop a horse safely. 

My early education was classical, and as much as there are things (the boot camp stuff -- do or else) that I totally disagree with .. I learned lots of good stuff from old-style cavalry trained officers. Like, having an independent seat. :) 

No one talked about positive reinforcement -- yet the classically trained officers were using positive relelases. Using strong gimmicks was forbidden, and horses were ridden in a simple snaffle for jumping and cross-country and eventing, a running martingale *maybe* allowed. 

I also remember the good training of our best dressage horse trained by one of the officers: after I won the national jr. dressage championship on him, I was allowed / ordered to show him jumping... we won!... he was versatile, in shape, and taught me how well-practiced dressage is the best foundation.

 Why I always wanted to ride, no one quite knows. Grew up in Bucharest, the capital of Romania, under a brutal communist dictatorship. There was no private property, the state owned and (mis)managed everything. Athletes, kids too, we were all quasi-employed, all training paid for, but we had to perform, or quit, and had to obey, or else. Not a lot of choice.

 When the communists took over 1947, they sent all good horses to slaughter, as they were considered a bourgeois tool of oppressing the masses. Horse people hid purebloods, the prized Arabians & TB's under the plow... so they would look like a poor man's workbeast, not a riding horse. Riding was severly stunnted.

 Except in the Romanian army. Oh, yes, they tried to stomp out the old cavalry, but keep in mind that the cavalry was active as late as 1947. My grandpa **fought** on horseback in WWII (got captured and sent to Siberia) 
So, they kept a few outposts of the "cavalry" -- for parades and such. The officers, all formally trained in classical jumping / dressage, were happy to work with horses, and hide from communism in their own little world with the horses.