Well, you are the guy with the Kim K. avatar, but I have to stop you there...

Most of the earlier KoF games had mini biographies for the characters with stuff like age, blood types, hobbies etc. If I remember correctly, the age range of many of the male fighters (especially the "archetypical" fighting game main characters like Terry, Andy, Joe, Ryo, Robert etc) ranges only between ~ 20 and 25. Everything over 25 is usually reserved for battle hardened war veterans (Ralf and Clark), or "older" (in anime terms) women like Mature, Vice and Chizuru (all in their late 20s I believe). Characters also did not age between games if I'm not completely mistaken. That excludes games that obviously take place in the "future" like Garou MotW.
So technically it's not wrong for Andy to look pretty young, when he's only 23 or so. =P