I may be sounding like a broken record here, but the answer to both of your questions (Randolph and Rachel) is evolution, that is: NATURE and EVOLUTION.
Randolph --- Like I stated in the reply to your question about women's butts, a big dick is one of the main sexual attractions for women. Just like the female fertility goddess statues we have from antiquity, there are male god statues that emphasize the phallus. In both cases however, neither endowment have achieved the status of being a species wide characteristic since they really don't provide an overwhelming survival advantage. In the case of big dicks this is probally more true - since many people have been wearing clothes for a long time due to the climate they lived in and it was not readily apparent to the chicks who was hung the best.
Rachel --- Nature has dictated that young people are sexually mature around the age of 13, that is; they are able to reproduce themselves. (( Actually, thie age has been steadily moving downward in modern time due to better nutrition and vitimins. Doctors and scientists have noted that many more are entering puberty at younger and younger ages, some as early as 9 yrs of age. )) Many primitive and ancient cultures recognize this and there are rites of puberty or passage to acknowledge the fact. Examples of this would be ceromonial actions such as the bar mitzvah and bat mitzvah for Jewish adolescents. After these rites of passage, they are considered to be men and women. The modern world really does not have a comparable recognition of this fact of nature.
So here we are now in modern times. Our modern culture has required that the end of childhood to be extended due to the need for more and more education, both formal and cultural, to prepare young people for society. You know that it wasn't so very long ago in our history that most young men and women had finished their formal schooling by the ages of 14 to 16. The young men left to work the family farm, or in some cases started their own farm. Others went to work as apprentices. Young women went to work in the occupations that were open to them: domestic service, secretary, teachers, factories, etc while of course many were married and starting families of their own. At the present time, the vast majority remain in school until the age of 17-18 and many of those go onto further education, requiring more years until they are fully accepted as contributing adult members of society.
So what is the status of our young people? On one hand, they have passd through puberty and are no longer children. Their bodies are just like "adults" though younger, AND, in a culture that values youth. Therefore they may just feel a bit superior to the "old folks". As children, they pretty much accepted adult authority. As young adults, they have developed their own mind set. Along the way, they have found many instances where adults were in error, and as the old saying goes: "familiarity breeds contempt". Sure. there are a lot of things they don't know. But that is it. They don't know that they don't know. What they know is that their bodies and their minds tell them that they are grown up, yet; in many instances they are treated like children. CONFLICT!
Now I have observed this conflict over many years and many families. I will tell you one thing I truly believe. If you have not pretty much taught children right from wrong and installed a true respect for adult wisdom by the time they are twelve, you are too late. "The gate is open and the bull is out!" By respect, I mean one that is based on your actions and wisdom, and not alone on punishment. Corporal punishment, within restraints, is fine for younger children as their reasoning power is limited. By the age of thirteen, discipline should usually be replaced by material punishment ie. loss of priviliges, restrictions, etc. This puts matters on a more adult level, that is - it recognizes their capacity for reasoning and places responsibility for their actions on them.
Hmmm, final answer
Young people are what we make them. If they grow up with good role models, they generally turn out fine. If there are no respected role models, they are not so good.