Now, as to the topic of controlling the onset of puberty, why the hell not. Our social structure nowadays is too complicated to grasp within our short childhoods, and we end up having to learn things along the way, often with unwanted consequences. (yes, we learn better first hand, but getting raped so you can learn what it is to be raped is just stupid and cruel)
The thing is, we have already outrun evolution. We are too advanced for our own biology.
Besides, delaying puberty would give most of us a few decades bonus in our life expectancy, since a large part of aging is triggered by sexual maturity. (as tested in worms by previous experiments)
Still, the biggest hurdle to this would be our technology. (politics will come later) As paolo has stated, we know very little of the effects that manipulating the onset of puberty has on the body.
Oh, and in the near future, we probably won't have to worry about deciding this before the child is born. Viral (or nanorobotic) vectors could be used to introduce new genes even in adult individuals.