That's not the only such example in García Márquez's work; in Love in the Time of Cholera, Florentino Ariza's love interest when Fermina Daza's husband dies is 12 years old, I believe. And she kills herself as a result of Ariza leaving her. I last read the book like six years ago, but I remember being somewhat taken aback but not overly disturbed by Ariza's 12-year-old jilted lover. I assumed that García Márquez wasn't literally advocating a septuagenarian having sex with pre-teens, and that her age was basically symbolic of the tragic side of young love, and that it helped distance the arc of the story from that of a fairy tale.
Nonetheless, her being 12 as opposed to, say, 17 didn't make that part of the story any more poignant. Quite the opposite, in fact, because the reader is so startled by the girl's age that her role in the story is easy to miss. The same is true of Memories of My Sad Whores.
In any event, the twelve-year old appeared to be of legal age in the movie version of Love in the Time of Cholera. I imagine they'll make a similar switch in the movie version of Memories. I'm not really going anywhere with this, but it's interesting to consider in the wake of Polanski-gate.