I've hit 21 with very little effort on my part, mainly thanks to my parents for lugging us 4 kids around the world with them. My childhood was rich with travel. My childhood passports are filled to the brim. As an adult, I have mainly traveled in the US, as well as Mexico and Canada several times (then France + UK this past summer).
Here is my current travel map:
Here are the countries I have currently visited (marked in red and bolded. Asterisk * means I've lived there) & the countries I want to see before I'm 40 are left in plain text:
Create Your Own Visited States Map