This question really shouldn't be taken seriously, but I will anyway.
There's no way you can tell. You might get 12 year olds throwing 7's down in Park City, Utah or Breckenridge, Colorado - but come to the PNW and you'll find 12 year olds who an just about throw a 3 but slay the powder/backcountry. Also, with the increasing number of people on twins, who's to judge who is or isn't a freeskier? If by 'on average' you mean the whole skiing population, obviously, the average 'trick' will be seriously low - like a 90 degree spin or something. If, on the otherhand, you mean a freeskier - well, I don't know what makes someone a 'freeskier' or 'gaper'.