The blog that talks about the test has some interesting facts and figures about vocab sizes generally - an excerpt below.
We've made two discoveries so far. The first is that, for native speakers age 18+, most people (74%) have a vocabulary size between 20,000 and 35,000 (13% below, and 13% above). Of course, this is for the specific subset of people who are Internet users and have taken our test so far.
Our second discovery is much more interesting, a statistic we haven't come across anywhere before. We calculated average vocabulary sizes for native English speakers for ages 15–32, which is the range of ages for which we have at least 100 respondents per year of birth, and discovered there is a remarkably linear progression from 23,303 words (age 15) to 29,330 words (age 32), which works out to an average increase of 355 words per year, or almost exactly one new word a day (0.97 words to be precise).What I find intriguing is that my age and the total I got tally with their suggestion that I am learning about one new word a day!