Among high school and college seniors it's common to claim that "the past four years have gone by so fast!," and make similar declarations of outright shock at the objectively standardized passage of time. Let's assume that they're telling the truth about the subjective time expansion, as opposed to merely taking a roundabout route to say that they care about their friends and will miss them. Why might the time expansion occur? There's plenty of research on this, explained by three competing theories:
Lack of Attention: We seem to recall events that we pay more attention to as being longer. For example, adding white static noise in an auditory detection task causes people to pay more attention to those intervals, and they are judged as lasting longer (see here). This one is a little controversial; some studies have found opposite effects. However, it is plausible that if students don't pay attention to what's going on, time may be perceived as passing more quickly.
Predictability: Novelty causes time perception to increase. For example, the first time a moving dot is shown to people for 480 milliseconds, they consider it to be visible for ~120 milliseconds longer, an increase of ~25% (see here). So if students get into a routine, they might consider time to be passing faster because they don't get this novelty effect.
Causality: The feeling of control makes events seem longer. For example, when people press a button to cause a 900 millisecond tone to start, they perceive the interval as lasting ~ 30 milliseconds longer than if the tone is started without their control (see here). So, if students make something happen at school of their own doing, they might remember it as lasting longer.
On this basis, if you want to extend your perceived tenure in college, you should attend more interesting classes, expose yourself to more randomness, and throw more of your own parties.
In fact, compared to "the workplace" (scare quotes emphasized), college has lots of time perception extending advantages: many new people to meet and new things to do. So if you think that these four years went by fast, get ready for the next four to go even faster.