I don't think that it is easier for a kid 15 or younger to get into top universities. In fact, the opposite is probably true.
That's my anecdotal experience, as well. I was wait-listed for my top choice school when applying as a "left high school at 16, following junior year" applicant. I ended up doing a year abroad rather than go to my second-choice school, and accepted for admission to enter as a 17yo.
DD will graduate high school at 16, and if she goes straight to college, start college at 17. I'd be fine with her going where ever she wanted. Graduating at 15 and starting at 16, maybe not so much.
In my own experience, taking a year off of rigorous math and science classes, on top of coming from a high school that didn't offer much in the way of rigorous science, negatively influenced my choice of college classes. I personally would rather see DD go straight to college than take a gap year.
