Adult vocabulary size appears to be principally determined by reading habits between ages 4 and 15.I took the Test Your Vocab quiz, but I can't say how I did because "it’s considered bad form to reveal your score or to ask others how they scored."
P.S. "Word-Hoard" is an Old English term for the words you know: "Words are useful to have, and to cherish as one of The Good People gloats over his gold under the hill."
P.P.S. If you're over 15 & want to expand your vocabulary, don't give up!
12 Ways to Learn Vocabulary with the New York Times
Wiki-How To Build Your Vocabulary