could not disagree more.
Believe it or not maturity is actually something that exists and there is no such thing as a 15 year old who is actually mature.
I completely agree that there are plenty of 15 year olds that have been in war and it has never ended well either. They also were never generals or leading anyone.
At best you might be able to find a boy king but even then it was never an elected official and during that time they weren't even given as much responsibility as ruling an entire planet.
Closet example I could think of is Alexander the Great but even then his mother did the real ruling until he was old enough. However in TPM we see Padme is the one who is actually in charge.
At 15 years old kids are still going through puberty at that time. You really want someone who is at the will of their hormones in charge of an entire planet?
For all you know the people from Naboo may very well complete puberty well before the age of 15 , they very well may be well into their adult life by 11 or 12 even. the fact is YOU DON"T KNOW !