I believe his father was a Cuban citizen at the time of his birth, making him ineligible under the Natural Born Citizen (NBC) clause in the Constitution.
Is there any evidence that that was considered the standard for NBC 50 years ago?
Yes his father was not a citizen, but his mother was and appears to have complied with the requirements of having resided within the US for at least 5 years.
The governing statue is Title 8 section 1401 subsection G
(g) a person born outside the geographical limits of the United States and its outlying possessions of parents one of whom is an alien, and the other a citizen of the United States who, prior to the birth of such person, was physically present in the United States or its outlying possessions for a period or periods totaling not less than five years, at least two of which were after attaining the age of fourteen years: Provided, That any periods of honorable service in the Armed Forces of the United States, or periods of employment with the United States Government or with an international organization as that term is defined in section 288 of title 22 by such citizen parent, or any periods during which such citizen parent is physically present abroad as the dependent unmarried son or daughter and a member of the household of a person
(A) honorably serving with the Armed Forces of the United States, or
(B) employed by the United States Government or an international organization as defined in section 288 of title 22, may be included in order to satisfy the physical-presence requirement of this paragraph. This proviso shall be applicable to persons born on or after December 24, 1952, to the same extent as if it had become effective in its present form on that date;
Thus according to this statue, Cruz was never in need of naturalization for his citizenship. He received it from his mother. Therefor, he is a “naturally born citizen”. ASSUMING that his mother who obtained a degree in mathematics (4 years?) prior to Cruz’s birth did in fact, meet the requirements of 5 years of residency, two of which after obtaining the age of 14.
It would be reasonable to assume absent any evidence that his mother graduated high school (18) and then went to college (22). That would be 7 years of residence after the age of 14.