Originally Posted by ColinsMum
Originally Posted by 22B
One concern is I was wondering if taking university courses (while officially being a seconday school student) could disqualify you from competing in certain maths competitions.

This is a valid concern, I think, and the rules are quite likely to change given the fluidity of the current situation, so it's one to watch. For the IMO at present,
Originally Posted by IMO
Contestants must not have formally enrolled at a university or any other equivalent post-secondary
institution, and they must have been born less than twenty years before the day of the second Contest
Unfortunately, "formally enrolled" is not further defined, though some countries (Canada turned up on my google) elucidate this as meaning enrolled on a degree-granting programme.

In another thread
this link was posted
Originally Posted by linked article
Larson is a member of his school's math, chemistry and programming clubs. He won the silver medal at the International Math Olympiad in 2007, and since his freshman year he has taken all his math classes at the University of Oregon .
Here "freshman" means 1st year high school -- 9th grade.
So that's one data point that someone can take university maths courses and still go in the IMO.