1.) Work and taxes are closely related: You get an income and a portion has to be given to the government. That has been in place since the founding of this country. Also, the government used to allow 14 year-olds to quit school and work because grammer school was only needed. We now have 2 years of high school, but there is talk about forcing students to attend all four years as most people without a high school diploma are not getting proper employments.
2.) Actually, a few states only allow 16 year-olds to have sex, and that's only between people their same age; 18 year-olds can be tried for statutory rape.
I think 18 is the mark as you can vote, buy cigarettes, and technically, if your parents say "Get the F out of my house!," you have no say in the matter because most laws recognize you as an adult. That's also the age you can serve in the armed forces. Also, all states allow marriages between 18 year-olds.
