Buster's unseen parents have become hostages in Dagon for years now; so the time skip made him eleven (in the beginning he was eight) and Ken sixteen.
It has also been suggested that Leroy was responsible for luring Buster's parents Timothy and Mercy Caldwell into Dagon. Timothy and Mercy are freed with the help of rebelling beast men, so they dramatically reunite with Buster.
In the day Buster leaves Africa, Ken swept a lot of tears.
End of story.
