I think it just means he became a father after a certain age.
There are many other verses that say something like "so-and-so was ___years and begat. . ."
and lists the children and which wife they belonged to.
I find it interesting that Noah was FIVE CENTURIES old when he became a father. I wonder how old his wife was. That would be equal to probably being about 50-years-old now, which is still a late age to father your first child, but five HUNDRED years old?!