How hard is to convert to developers adults with training in other areas, but with presumed cognitive skills suitable for programming? I am thinking of people of 35-50 years old, that would be intelligent enough (i.e., there would be just a percentage of this cohort that would be fit for becoming developers), but who, from various historical and personal reasons, work in industries where the prospects are less interesting than in programming.

Are there any studies showing how the potential to learn programming decreases (or not) with age? I have looked on Google Scholar but I found nothing.