In 2011, a dad in Paris filmed his 1-year-old daughter trying to swipe a paper magazine like it was an iPad. That baby is 16 now. Kids like her are the reason Apple is putting a touchscreen on the Mac this Wednesday, after two decades of refusing to. And she was pretty normal for her age. In 2011, fewer than 1% of American kids under 8 had their own tablet. Six years later it was 42%. The oldest of those kids turn 17 this year, which means they're about to go buy their first real…