I feel like I should know this, but what’s the rule(s?) governing when 2yo’s can race for the first time? I noticed when I sent out my first pack this last year that the older ones were able to race earlier, but as I recall, at least one of them was allowed to begin racing before his official birthday (though I might be misremembering). Would someone mind es’plaining? 
Just like in RL, a horse doesn’t have to be a certain age to run. Just whatever age they turn that year.
So technically, a December foal born this year (say a early foal born Dec 30) can run as a 2yo when it is only 1.5 years old. Not ideal though and I wouldn’t run it.
2yo races don’t appear on the schedule until April each year, which is probably why you remember older horses starting first, and babies running before their birthday.