You just gave the definition of "cannot". Those circumstances will never happen, they're pure hypotheticals. Sure, hypothetically I might be able to play competitive tennis against Nadal. Practically, though, that'll never happen, I cannot and will never be able to do that - pretending otherwise is just naive and purely theoretical discussion.
Still though, we could ask how many people in the entire human population could run under a 4 minute mile with any amount of training, time and resources? Obviously more than have done it, but how many? Certainly not remotely close to everyone.
If the claim was merely that math comes easier to some than others - again it would be an uncontroversial claim and i would agree with it.
However, my reading of the original comment was that a good portion of the population literally are physically incapable under any circumstance, including the silly hypothetical circumstances i laid out, to learn algebra. I think that is false. It sounds like you do too. So i guess we're in agreement.
Not exactly. I read the original claim that they are "incapable to learn algebra even in very good/way above average (but still realistic) circumstances".
I think most people agree that there are extremes. There probably exists a small number of people who literally cannot (just like how 1 in a million could probably teach themselves calculus at age 10, also exists). However it's a big jump to conclude that even a small percentage of the people at your college cannot in the literal sense - i.e. if their life depended on it, they had all the resources they could want, they had no other distractions.