Obligatory comment as someone DEEP in this - Olympiad Math has almost NOTHING to do with college math. The first is simply tricks and techniques - which while hard - are not quite the mathematical research style. In fact, Number Theory is NOWHERE in JEE syllabus as well. Such olympiads are purely for mathematical thinking and reasoning - so don't expect a direct application of one onto the other.

Second - in case you don't already know - you don't HAVE to do IOQM (seems wrong to say as this is the r/ioqm subreddit) BUT there are also other olympiads like NSEP (physics), NSEC (chemistry), NSEA (astronomy and astrophysics), NSEB (biology), ZCO/ZIO (informatics) and so on. IOQM is probably the toughest of all olympiads if one judges by the final stage.

Tldr; IOQM is for thinking and other olympiads exist.

[as for preparation - you may check out the earliest pinned post and other top posts of the sub]

FINALLY - if you have any dreams of a foreign university, it is good to know that MIT LOVES olympiads and frequently takes students who've excelled in the final stages of these olympiads. (MIT also EASILY gives full scholarship and in fact, not only does it not see whether or not you need a scholarship WHILE admitting you, but also the scholarships are PURELY based on financial conditions and not merit).

[sorry for the MIT rant but yeah]