TITLE: How to test whether I am suitable to pursue mathematics?
QUESTION [21 upvotes]: I am a high-school student. I have developed a recent affection towards mathematics (especially proofs), although I was always into logic (I've been a programmer since the age of eight). Now I am worried whether I will succeed in mathematics as a career. I have an IQ in the 99.7%ile in India and always score approximately 150 in IQ tests. (I know IQ is irrelevant.)
To judge whether I am capable enough to be a mathematician, I have set myself a challenge: if I clear the entrance exam of ISI, only then shall I pursue mathematics. (Sample ISI exam questions.) I want to know from current math grad students, professors and teachers whether this challenge will be good enough to test whether I have the ability to pursue mathematics as a career. If not, then how can I judge myself?
I don't have access to olympiads, though the subjective questions of ISI are considered on par with InMO, and clearing the exam is also considered a big achievement in India.

REPLY [4 votes]: "Am I suitable to pursue mathematics?"
The answer is a resounding: YES!
If you already know that you enjoy Math, you are in the privileged minority. Appreciation of mathematical inquiry is something you can deeply value.
It's hard to say exactly what the experience might be like for you, but I can share my perspective:
I'm not the world's best mathematician by any means, but I got along, and when it came time to decide on a major, I picked Mathematics (along with Philosophy). It was a challenging curriculum, but I'm very glad I made this decision. It has opened up so many doors for me, because nearly any other quantitative inquiry is founded upon Mathematics. 
It strengthens qualitative reasoning as well, with the heavy emphasis on logic and rigorous proofs. Even though I don't often use it in the same manner I was formally taught, the skills and perspectives from my undergraduate math education are relevant nearly everyday, many times over.
So again: Go for it!! If you love it, you don't need permission. :)
If you're looking for further reading on this: a professor once told me about G.H. Hardy's A Mathematician Apology. 
I highly recommend it if you want to learn why so many mathematicians love math. It's a short read: here's a PDF.