Everyone people make the relation and their relation is based on age. But in this case age is very small and relation is very big. Family relation and age gap is most of the time confused . There is no parameter to calculate the age. But for every relation there must be standard age.
But if you heard that a guy who became the father at the age of 23 year old but he became the grandfather after one week . When you will think about this you will raised your eyebrows and and ignore it just to think he is insane. But before making such a thought read this article.