When Edward Holgate first took on the secret identity of the seemingly vile Baron Trotha he had the best of intentions. By sending his Ironbones to murder the corrupt and the evil he meant at first only to purge the Kingdom of Vallermoore for it's own good. He was content to serve King Montor; he respected him and knew he could rule well, and with two daughters, Faith and Emma, and as there was a long tradition in Vallermoore of accepting female rulers, he had no chance of taking over the Kingdom. It was true that Emma was just a baby and that the Queen had perished in giving birth to her, but the King was healthy and his daughter Princess Faith was old enough to rule after him. Two things changed this dramatically; his discovery that Princess Faith was greedy and in his mind, not fit to rule, a kidnapping solved that problem in the short term. The other was the cancer that soon afterwards killed King Montor; the then three year old Princess Emma was crowned as Queen and as she was far too young and needed a capable Regent. And who better then the King's Chief Wizard, Edward Holgate, for the task?
Reluctantly, he had Princess Faith strangled and buried secretly in the woods with no grave marker upon it and set about ruling as Regent, and, for his own enjoyment, studying the waters of the Sorcery Springs Geyser Basin . It was when he was studying the warm waters of one of the springs that he realized that it was a true fountain of Youth! He could sell this potion for a vast sum, everybody would want it. And then he realized the dangers of what that would cause in the long run. Mass overpopulation. Wars in some regions for territory that rolled on and on and on, with genocide for the losers. Famine in others as the number of mouths to feed outweighed the food that could be grown or fished or hunted. As Regent he had enough money anyway. He did take the spring water for himself, and then had an idea.
When the five year old Emma reached the age of eighteen she would be able to rule in her own right, so why not stop her growing up? Not by murdering her, he could not bear to kill a five year old child and everyone would suspect him of the killing anyway. But by using the spring water of youth to keep her forever as a sweet five year old girl playing with her toys and happy with her life. He gave orders that she was not to be educated more then a five year old would be but over time, one of her teachers took pity on her and secretly educated her so she was as clever as any aristocratic woman of her age. Something that to her annoyance she has had to hide for decades, as if the Regent discovered she had the mind of an adult instead of a child he might well arrange her death rather then give up power.
In public she has to act like a sweet five year old, in private she can act like an adult and if she meets the PCs will beg them to cure her and will offer rich rewards in return, such as the waters of Life itself so the PCs need never fear old age.