What should I study when I grow up?

Here's my dilemma. I'm currently 15, doing IGCSE (first year) and I really don't know what to study when I get into college. Thing is, my marks are pretty high. I have an 18 in Extended Mathematics, 17 in English Literature & First Language, 18 in Spanish Literature, 17 in History, 17 in Geography, 16 in Economics, and well, a bad 11 in Coordinated Sciences. I would say my marks are rather high, and I'm definetly in the top 30% of the whole grade. I, however, do not know how much will my marks influence my entry opportunities to high-prestige universities (e.g. Manchester University, Yale, Harvard, Cambridge, Oxford, Princeton, etc.), I'm obviously doing IB when I reach 11th grade, but I'm having doubts on what to study. I'm really good in Mathematics (the teacher has said to me that I should follow Mathematics High in the International Baccalaureate), really good in Literature (both narratives I wrote in English and/or Spanish got 20's) althought my favourite course is History. I thought I might study either Literature, Philosophy, Businesses Management, or even become a Mathematician. I'm definetly gettin a PhD in any field I decide to study, but I cannot make my mind up. Any suggestions?