The summer after graduating high school everyone and their mother will tell you "enjoy college it's the best four years of your life!" Which if you really think about, is kind of sad. I think their point, though, is more well-intentioned.
College is intended to be a time to challenge yourself intellectually and specialize in certain skills. And it is, once you're in your major and taking all the classes within your major. However, there are some aspects besides this specialization that really are a once in a lifetime opportunity.
Sticking within the realm of school, there will never again be a time in your life in which you can take an in-depth course on a subject that will most likely be of little use in your professional career. Being able to take a course on astronomy or anthropology or whatever gen. ed. or elective you choose is a great opportunity to learn about a topic that actually interests you outside of your major. It is a way to broaden your horizons. And unless you're willing to pay a large amount of money in the future for just one course, the best way you will be able to learn about an interesting subject is through reading articles and watching videos online; and let's be honest, without a professor to grade you, you won't be reading these materials as intensely as in a classroom.
Outside of school, college campuses are incredible places as well. Never again will you be surrounded by thousands of people, most of who are within four years of your age and have similar interests. This is a great opportunity to meet so many people and make friends. This is why, if someone might have struggled socially in high school they almost always find a group of friends in college. There are so many people to get to know; all of whom are smart enough to be accepted into your college. Everyone you run into, whether they are in your major or not, is capable of having an intellectual, in-depth conversation, which is another great aspect of the college
So when all of your aunts and uncles tell you college is the best time of your life, they're not saying it was their "peak". Instead, it's a time in your life when you can learn about almost any academic subject and at the same time meet a huge amount of different people and make tons of new relationships. It's a time and place that cannot be reproduced, so make the most of it.