If it were a state marriage where it was basically a marriage in name only with limited or even no cohabitation involved, that wouldn't be an issue.
An episode of "The Simpsons" got away with having Bart get married to a older girl, through emphasis upon Bart's relative ignorance of the particulars of Adult relationships.
The Tom Hanks movie, "Big", if examined carefully was actually fairly risque in this regard. A twelve year old boy, aged by his wish into a thirty year old, takes up relations with a woman at least twice his biological age.
Instead of being reviled for depicting what could be misconsrued as a predatory relationship, it was lauded as a tale of innocence and the wonder of first love.
So it would depend upon the circumstances. How you manipulate peoples perceptions into accepting the situation.
For instance, a history teacher once pointed out to us that the average adult in celtic times was less then twenty-five years old. And most Adults within the usual war clan or hunting party were approximently sixteen years old.
Back then, if you hit your thirtieth birthday, you were considered to be quite elderly.
So if your character's co-horts in this royal court are all teenagers, it would be viewed as a bunch of teenagers doing what they do. And that has always been allowed, (more or less).