Are you not aware of people who are "tone deaf"? All the training in the world won't get them to recognize tones. It's similar with me and recalling pictures or visualizing. My brain doesn't do that. I am unable. Understand?
Actually, I have seen people who were supposedly "tone deaf" and, as the saying goes, not able to carry a tune in a bucket in fact be trained to carry a tune in a bucket. (Did I mention I was a music major?) However, some people undoubtedly have more of a propensity for carrying tunes, drawing pictures, writing code, etc. Some of that propensity may be genetic, some may be environmental, and everything seems harder to learn as we get older.
I agree that the vast majority of people with basic math skills (add/subtract/multiply/divide) and able to read at a junior-high level could learn to program computers to some degree. But there certainly are those with a greater innate skill, propensity, desire, etc. who become the really good coders (not me!), and there are undoubtedly those who don't have the innate abilities required and lack the desire to acquire those abilities, assuming they don't in fact have some phsycial/mental defect that gets in the way of such learning.