Schubwa is correct, not only about very early season, but also very late, according to Mammoth's marketing director Joani Lynch. She says the 40% overall snowboard proportion at Mammoth is higher at the start and end of the season.
In line with Schubwa's comment, I'm almost never at Mammoth on the early WRODs, last Thanksgiving being the exception. I didn't consciously notice the proportion, but I did note the time a few boarders sat down in a less than ideal choke point on Broadway.
I'm there a lot in late season, and I don't notice the proportion much then either where I'm skiing. But I have noted, and taken numerous pictures of, the late season Saddle Bowl terrain park which is very popular and I'm sure mainly boarders.
So yes, we should lighten up on the young boarders, as they seem to be providing most of the incentive for ski areas to extend their seasons, at least here on the West Coast.