<p>I had a high school classmate who was taking grad-level math classes by their senior year of high school, but I always thought that pretty rare.</p>
<p>I would generally advise against rushing through undergrad, especially if you have aspirations towards grad school - as another mentioned, there is more to grad admissions than grades and GRE scores, and it takes time to build a record of research and to develop relationships with professors. You CAN do it, but you need to remember that there is always a cost - perhaps the lack of research means you get into a masters instead of a PhD program, or you get into a less competitive school than you might otherwise have been able to, or perhaps you have to pay more (or all) of your educational expenses rather than having full financial support, or perhaps you enter the wrong program because you lacked a strong mentor in undergrad who could help identify and get you into the right program for YOU. There is, of course, no way to be sure - anything is possible. I just would recommend going slow and strong, rather than fast and weak.</p>