Caleb was born in 1992, and in Kenya everybody born before 2003 didn't have the official registration of the birthday in the Hospital, which started to be a must after that date.
Children didn't have ID till when they needed for the first time (for the most part of athletes, when they had to compete in the National School Championships, where every participant has to show an official document).
So, when they needed, they had to go to the office of the district for asking the Birth certificate. The official asked "in which class in the school are you ?", and, according to the class, they gave the official year of Birth. The day was the day of the request.
But in many cases, when we speak about boys living in small villages on the mountains, they didn't start primary schools when 6y old, but when 8 or 10 (when, fo example, the school was very far from thei house). This fact explains why, in the most part of cases, in their passport the age is not correct.
The situation for new generations now is completely different, and I think that everybody born in the last 10 years has perfect documents, very correct, like in Europe and Northern America.
Also in Asia (China, for example), we often find the same situation. We need to know the reality of small villages without any official structure, and without specific facilities and equipments, for understanding this diffused situation, before thinking everybody is a cheater because of the possibility to win medals in athletics cheating about the age.