There is a certain logic when you suggest people would be more law-abiding if there were fewer laws. Naturally the problems start when not everyone agrees what the laws should be. In fact you might say there's serious disagreement on a lot of them or in some of the details.
You are, of course, correct that the problem is a lack of consenus on how many laws are necessary and exactly what those laws should be. Obviously, some laws are necessary in order to maintain a civilized society. Without any laws at all, we would digress into anarchy. The 64,000 dollar question, however, is whether or not we need the number of laws we've got in order to maintain a civilized society. There are thousands and thousands of federal laws and probably just as many, if not more, state and local laws. Not only that, but many of the laws currently on the books are very complicated and difficult to understand. For example, a very prominent federal law which has been the subject of much controversy recently (I won't specifically name the law in order to avoid digressing into partisan politics) is well over 1,000 pages long. With such a long and complicated law, it is nearly impossible for the average person to even know exactly what is in it, much less understand all of it.
I am of the opinion that most new laws have crossed the line from maintaining a civilized society into being unnecessarily intrusive into our lives and personal freedom. It seems to me that attempting to legislate all of society's problems away results in turning otherwise law abiding people into criminals. This is all the more we should probably discuss this particular issue though as we're getting away from the original topic of the thread.
As to the detail in laws, where the devil dwells, the question of college students and by extension, high school students (why not?), is a question of age and also of place. How old is an adult? Or rather, what should we consider an adult to be? Sixteen, 18, 19, 21 or something else?
Again, you are correct that the crux of the issue is defining at what point someone is mentally and emotionally mature enough to be entrusted with the rights and responsibilities of an adult. The problem is that there's no really good answer to this as people mature differently (if at all). Insofar as firearm ownership is concerned, I've known grade school children who were, in my opinion, trustworthy with a firearm but by the same token I've known people well into their sixties who I wouldn't trust with a Super Soaker.
The fact of the matter is that we have to draw the legal line between child and adult somewhere. 18 years old happens to be where we've drawn the line, yet for the first three years of adulthood we tell people that they're old enough to be held accountable for themselves and punished as an adult if they break the law, but that they're not yet mature enough to enjoy all the rights and privleages of an adult. This is my point of contention: if people under the age of 21 are, by and large, not mentally and emotionally mature enough to own a handgun or drink an alcoholic beverage, then they are also too mentally and emotionally immature to be married, enter into legal contracts, serve in the armed forces, live alone without the supervision of an adult, get a driver's license without their parent or guardian's consent, vote, or be tried and sentenced as an adult if they commit a crime. If we really believe that people are not mentally and emotionally mature until 21 years of age, then we should simply raise the age of majority for everything to 21 rather than deny 18-20-year-olds some of their rights while saddling them with all of the responsibility.