He possesses youthful vigor, as do his parents
He’s a karate master, like the Karate Kid. Does this explain Ralph’s youthful appearance? It’s not that he doesn’t care about maintaining a healthy lifestyle; he just believes he has a genetic advantage. He made the point that his parents, who are both in their sixties, “look young for their age,” and that he, too, “has a youthful vigor.”
He was allowed to portray younger characters because of his youthful appearance as an actor. His love interest was just 15 while he was producing “Karate Kid Part III” when he was 26. The screenplay had to be changed in order for it to be platonic during production.