I think it's still telling that none of them took the oath entirely seriously. Though it's possible that Dorukan used that age bonus to his Wisdom score to realize that continuing to completely flaunt the oath was a bit of a jackass thing to do, especially when Soon never broke it. Still, Lirian and Dorukan were still continuing their relationship, Girard setting his message trap to alert Serini, and Serini sneaking into Dorukan's Dungeon do show they didn't really care about the oath that much.

Also maybe Dorukan didn't want Serini on his premises for a reason outside the oath.