Last year I tried Single Variable Calculus (very good course) and look some videos of Multivariable Calculus on MITOCW and I cover almost all the material. So, when I took that course I realised I want to learn about mathematics. I want to be a PhD physicist (and I know that it cover a lot of Advanced Mathematics), but I don't want to learn mathematics just to do physics, but also for DOING mathematics. I like very much to learn few concepts in new subjects than learning deeper and boring things about the same theme again and again. So, what are the best sources for learning mathematics to a 16 year old by my own? Remind I know calculus. I hope for your answers.