Any prior trauma that would have caused this issue?
I am not generally a big fan of running to PTs due to pain that is unrelated to a specific injury or medical procedure. My general philosophy is PTs are great for fixing injuries but the greatest for just fixing pain. I will qualify this with the fact that my wife just finished PT Assistant program and we are in agreement here. I have a good friend that is also a PT and she quietly whispers that advise too. My wife and I also have had surgeries that required PT.
So, that being said, at your age I would guess something is out of alignment or something is damaged due to something being out of alignment.
I came down Barr Trail (after the incline) and the top of my knee was hurting a lot the next day. Iced it. Motrin 3x a day-10 days. Nothing. Went in to a sports medicine chiropractor and he felt around the kneecap and felt that the tendon was misaligned. He worked it a bit and pushed the tendon back in place. In and out in one visit. Advised it would be sore for a bit then should start feeling better. If not, could use one or two more treatments. Few days later, 1000% improvement. He advised if I kept running on it, I would have torn the tendon. (In other words....listen to your body).
Now granted, I saw Dr. Leahy who invented Active Release Technique so he's da man. I would look into sports medicine doctor but highly recomend someone who is trained in ART.