What determines the tonal range of a person’s whistling? Is it the volume of the mouth at various tongue positions, or is it more complicated than that?
And do men and women (on average) have different whistling ranges?
And do children and adults (on average) have different whistling ranges?
I hope you get answers to this. It’s off beat enough to be interesting.
Id like to know what makes some people good whistlers, while most others suck. (Or more accurately, blow?). 
The pitch of a whistle is primarily a function of mouth volume–which, as you said, is largely controlled by tongue position.
There are other factors that play a role, though:
Your embouchure (lip position or “holding your mouth right”) limits your range, for one thing. Higher pitches require a tighter embouchure to get a clear tone, and it’s possible to bend the pitch slightly by moving the lips in or out. When I whistle on inhales, I notice a tendency to whistle a half-step to a full step higher because the air intake draws my lips in tighter.
Moving your jaw forward and down will also increase the available volume of your mouth, and can extend your range to deeper notes, as long as you can still maintain airflow and embouchure.
All this applies to “pucker” whistling–there are other ways to whistle, some of which work very differently.
BarnOwl, I don’t know what makes some people better whistlers than others, any more than I know why some people are better singers or have greater talent for a given instrument. Fine control over lip and tongue muscles is a factor, though, as is a good sense of relative pitch. You have to practice, too, like any other musical endeavor.
Huh. I always thought that my whistling range was the same as my singing range, because I can’t seem to whistle much higher/lower than I can sing. I guess I just don’t really know how to whistle.
If you’re short and can at least whistle while you work, you might have a future
with a certain motion picture studio.
Balance, thanks for acknowledging my question, even though you can’t answer it.
I think an ENT doctor could tell us what vocal cord features predispose toward a good voice, but I wonder if any MD or anatomist could do the same for good whistlers. Maybe a very smart whistler?