Whenever I see someone suggest that refraining from racing 2YOs would reduce the incidence of breakdowns, I wonder what would happen if they spent some time examining charts from “back in the day.” 2YOs were sometimes raced as early as January, and March wasn’t unusual at all-- and they went on to race for many years and substantially more starts than they do in the current day & age. Some didn’t start until later in the year, and some didn’t start until they turned three. One would presume there were reasons their trainers handled them the way they did, and that they (quite successfully) let the horses tell them what they were capable of doing.
Prohibit racing until age four? Good heavens. I am of the mind that we might be babying horses TOO much, not the opposite! There are a myriad of reasons why horses don’t make the number of starts they used to and why horses break down, but ‘racing too early’ almost certainly isn’t one of them.