It was brought up in an interview after Cheptegei raced in the Netherlands this weekend and his manager and accidently mentioned that he is 24 and not his official age of 20.
https://twitter.com/OlympicStatman/status/801519986506338305
http://www.ad.nl/offside/winnaar-zevenheuvelenloop-cheptegei-vier-jaar-ouder-dan-gedacht~ae9eb5cd/
Has any athlete ever been found guilty of age cheating?