Even "who is the first president" knowledge shouldn't be a bar to voting. Do you think they offered this literacy test in the native languages of all taking it? Do you think all people in the US had the opportunity to learn, in their language, the history of the country?
At the time there were systemic barriers to education that meant that many folk were probably not even taught who the first president was. Let alone how old you have to be to be president.
That isn't actually all that clear cut. I'd agree that it is probably a bad idea, but there is potential that the results would be better if voters understood the system that they were delivering instructions into.