OK, but what about the boys? Well, the youngest King was Henry VI, who was 8 months and 25 days old. I guess it takes us boys a little longer to mature than the gals (grin).
Elsewhere in the world, there were also some young rulers. I would say that the very youngest sworn in as ruler had to be Shah Shapur II back in the year 309. Persian nobles, according to the legend, placed a crown upon the belly of King Hormizd II's widow. She was carrying a baby and the fetus was crowned King!! Now, I want to know how they knew it was a boy??? There were other's who were crowned the day they were born, but I believe no others were crowned before birth.
OK, I sure hope my