I have TMJ as a result of a car accident that happened to me about 15 years ago. I'm supposed to wear a night guard when I sleep but never have. I also have had a dentist tell me that I grind my teeth at night.
With that said, what you described with the soreness in your temples and neck could very easily be from grinding your teeth. I read somewhere that when people grind their teeth the pressure that they bite down with can be very intense.
I know that I wake up probably four days out of the week with some sort of headache and I CONSTANTLY have different pains in my jaws along with clicking.
I don't think there is any particular age to be diagnosed with TMJ. You very well could have that. Next time maybe mention it to your dentist and get his/her opinion. I think, though, that from what you described, it's all related to the grinding of your teeth, especially since the headaches have gotten worse since you've lost the night guard.