Back in the day, old timers often recognized an officer's entrance into policeland based on career events. You had to have your first fight, first foot pursuit, first trip to the emergency room (as a patient), first specific type of investigation or whatever. Each department and each veteran officer has his or her own doormat to policeland.
Where I have concern is that some rookies try to push their luck in gaining these achievements. There are some things in life you can't push or create. Be patient. This too will come with time.
The most bothersome young officer is the one that becomes jaded too fast to experience the process. He is matter of fact, says, "This stuff is boring," and downplays events to impress others with nonchalant behavior. All the time, he really wants to burst with the exuberance of the job but can't do it because he is playing the cool card. Hint here: Enjoy the trip in policeland.
I have a different take on things. When the most mundane things to a "civilian" take on a decidedly law enforcement spin, this is when I believe you are about to enter the metamorphosis from rookie to cop. As a civilian and even a rookie you will do or say certain things in clearly identifiable ways. Real cops don't act and talk in the same way. Here are some examples of how you can tell if you have lost the innocence of life....
You can't drive down a street without having some story or tale of a call you rode there. The last time I was in that restaurant I had a robbery call there...