The fact that this game is interesting—as opposed to trivial, or impossible— suggests that humans have names for 220, or one million, things in their world. If humans only had names for one thousand things, then ten questions would suffice to specify any one of them; if humans had names for one billion things, then 30 questions would be necessary.
By tradition, a game of 20 questions begins with the fixed ternary question
Traditions like this begin because experienced players find that they always start the game with the same one or two questions, reflecting the two or three broadest conceptual categories in their model of the world. The fact that people begin the game by asking "animal, vegetable, or mineral" suggests that they organize their world like this
everything | +--------+----------+ | | | animals plants non-living things
When I play 20 questions, I don't find the "animal, vegetable, or mineral" classification so useful. Instead, I begin by asking
which suggests that I organize my world as
everything | +------+------+ | | man-made natural | +----+----+ | | living non-living
This probably reflects the ascendency of technology in our lives over the last 100 years.