Whoever wrote that story probably just didn't stop and think about what they were saying exactly I doubt that he/she was deliberately implying that the parents had sex at ten years old.
Personally I've never felt the need to give the exact age of any of my characters, I usually just say what stage of their life they're in (high school, collage, middle aged, retired etc.) and let the readers decide what a logical age is for them. Or even in some cases, whatever age makes them the most comfortable. That's one of the great things about the writer and reader relationship, and how creating a great story can be a collaborative effort. Any decision that the writer chooses not to make is left in the hands of the reader.