Ethiopians lie about age all of the time to compete in World XC Jrs in XC and track. It is standard practice.
I just turned 46, and know from a very reliable and close source that Geb is about the same age as me.
My wife and I hosted exchange students for 5 years. Many students were as old as they needed to be to be in the program. Birth dates on passports from other countries are what the person says they are. We hosted a guy that claimed to be 19, he was 15 - 16 years old. He lived in a town/village with a couple of hundred people, both of his parents were illiterate. His mom didn't give birth to him in a hospital, she gave birth to him at home, there were no hospital records, no record at the "court house". So when it came time for him to get a passport, guess what ... he provided his birth date which, conveniently, allowed him into the ESL program.