Ruth 4:22

And Obed begat Jesse
The Bethlehemite, the father of David:

and Jesse begat David;
the Targum adds, the king of Israel; and so the Syriac and Arabic versions add, the king; from whence it is by some concluded that this book was written by Samuel, not only after the birth of David, but after he had been anointed king by him: here being but four generations mentioned, from the coming of the Israelites into Canaan, to the birth of David, which was three hundred and sixty years, each of the four persons, Salmon, Boaz, Obed, and Jesse, must beget a son when one hundred years old and upwards; and which is not at all incredible, as appears by instances in later times, and therefore not at all improbable, that in those ancient times men of sobriety and good constitutions should have children at such an age.