old enough to be someone's father
old enough to be (one's) father
Of a man, much older than one, especially 20 or more years older (or around the age of one's actual father). Used especially when referring to a man who is or might be in a romantic or sexual relationship with a younger person (especially to indicate that the speaker thinks such a pairing would be inappropriate). How could you find him attractive—he's old enough to be your father! Everyone raised their eyebrows when they met Mark's new husband, as he's old enough to be Mark's father. But they do seem very happy together.
old enough to be someone's father (or mother)of a much greater age than someone. informal
1997 Nelson DeMille Plum Island He was probably old enough to be their father, but girls paid attention to money, pure and simple.