They’re both grandfathers, which seems preposterous until you do the math. When the groundbreaking documentary “Hoop Dreams” hit theaters in October 1994, the two subjects, Arthur Agee and William Gates, were 21 and 22, respectively. William’s daughter, Alicia, made her surprise appearance an hour into the film, just as William was beginning his junior year of high school. Alicia is 30 now and gave birth to a girl last August. William, 48, goes by Paw Paw. “At first, I was like, you’re too young to have a baby,” he says. “Then I said, ‘Well, I had you when I was 17. I guess 30 is OK.’ ”