I was going to stand up for the "kid" - until you added the background...
I was giving beginner rider lessons at the age of 13, but I was also taking more advanced lessons myself. I rode both western and hunt seat and showed in open shows and a hand full of rated H/J shows. The $$ I earned from giving the lessons that I gave, paid for my own more advanced lessons AND the showing. I worked with a variety of trainers/instructors from the ages of 12-21 - western horsemen/women, hunt seat and dressage (several were international competitors or had trained themselves w/ big name trainers/schools). We had and also started other horses at the ages of 18-24 months but I was a pretty small girl at that time and they didn't get jumped or worked excessively hard or for long periods of time. They were started for about 30-45 days of ground driving and riding, then turned out for a year. Brought back in and did another 90 days or so of under saddle work after they turned 3, then back out to "turn out". Our personal horses didn't have large pastures (we only had 6 acres), but they weren't stalled while allowed to grow and be babies. Several years we were able to pasture where I started colts for a couple of other trainers - so they were out w/ other horses their own ages and running/jumping/playing... The 2 yr olds didn't get a lot of pasture riding, but the 3s on up - did in the time frame they were up and being worked. I don't remember anything we had being started over cavaletti or jumped until 5/6 yrs of age. However - if a bush or ditch was in the field, WE DID JUMP that - even on a 3 yr old, but we didn't go out of our way to do it or make a regular practice of it... Just as often, the horse was stopped and asked to step one step at a time down into the ditch and up the other side. A 3 yr old also had a rope swung from his back and might be asked to stop and back when a yucca plant was roped (there were LOTS in CO then). I didn't ever rope any cattle off of any young horses myself - didn't have the cattle and really didn't have the hand/eye coordination either then.
Miss the "cowboy way"... though I generally was starting our ponies that way when my children were riding. Currently our grandchildren aren't riding yet, so ponies are going almost to maturity right now before getting a lot of ground driving due to time/work constraints and still working on getting everything set up here on this new property. It was EXCITING to me, to finally finish the round pen my SIL and I started putting up in March! Have a 5 yr old gelding who hasn't yet been introduced to harness or started ground driving yet and his pasture mate that was started ground driving and pulling "logs" at 3 yrs of age - who has yet to be hitched to a wheeled vehicle! He's going to be 6 in Feb...