What is theorized to be impossible is learning a language as an adult if you did not learn a language as a child. That is, if at age 20 you know 0 languages then you’ll never be able really learn a language. For obvious reasons experiments in this regard are few.

My conclusion is that some people simply can’t learn algebra. Be it genetic, environmental, lack of intellectual fortitude, lack of “intelligence”, or any combination thereof it is simply the case that some people can’t learn algebra.