It’s very optimistic to hope that many off-the-track Thoroughbreds could find homes with young riders. In general they are not desirable as riding horses for kids (though there are exceptions, and Thoroughbreds are among my favorite horses to ride, as you can tell from my screen name). Retraining OTTBs is not for the faint of heart and generally not for kids. Some of us love the Thoroughbreds, but most people prefer something quieter so that they don’t feel they’re taking their lives in their hands every time they get on.
BTW, the life expectancy of most horses is around 30, though some can die of old age as young as 24, and I knew one Thoroughbred who lived to 46, as documented by the US Jockey Club.
I'm going to disagree. My wife have three off the track Thoroughbreds and one Oldenburg with which we event. After having been in the track environment and on race courses they seem to me to have much more confidence and independence than the warmbloods. They become "bomb proof" much more quickly than the horse that spends its life in a stall and indoor arena. We vacationed at the White Stallion Ranch in Arizona when the mount they gave are kid was an off the track Thoroughbred, it did not surprise us much.