At 17, it's probably not an age spot. And it is also not in a spot that gets sun burned or anything like that. It's likely hyper pigmentation that may come from the area being rubbed with the crease of your body or clothes. Here is what I would do since it's just a darker spot of skin and is not causing any other issue . . . keep your eye on it and at your next annual well check or time that you are at your doctor, show it to them. If you want to get into see a dermatologist, by all means but know that is not the easiest specialty of medicine to get a quick appointment with. And this doesn't sound like something too concerning at this point. If it changes, then see a doctor sooner. good luck