The maximum score one can get is 45,000. The highest I've seen is in the 43K, but that was an older person on a religious forum (= well-versed in archaic language).
Anything over 10K, for non-native speakers, and you can give yourselves a pat in the back. I also put down money that if you retake it after a year here, you're going to score much, much better.
Older certainly does work to one's advantage, especially when combined with a lifetime of reading tons of fiction. My experience is that forum roleplay adds greatly(see below), especially if one does a lot of historical and fantasy, and tends to research heavily (which I guess would qualify as well versed in archic language). A keen curiosity, Google Fu, and Wikipedia addiction have to help as well.
My estimated number was:
42,900 (likely because of all the above).
Of course I know of very few people besides writers who might get to use nearly that amount of vocabulary in real life (people tend to back away from you when you do). Certainly I don't. So I took the test again, counting only words I actually use in real life (without getting strange looks) and came up with:
That's where roleplay really shines. Taking it a third time, I included all the words that are actually in active use in my roleplay vocabulary, and I got:
I'd say that is quite a testimonial to the affect of roleplay on vocabulary.
And yes, my muse wanted distraction this morning.