I applaud you, mom, for discovering your son has an issue and for trying to get him help. Being a teen doesn't make him too old to get help, but it might make it a bit difficult to get people to take you seriously. Be sure to tell the school district that you think your child has auditory issues within the Sensory Processing Disorder Spectrum--that will make more sense to them. My daughter has SPD and has been receiving services through the school district since she was three years old for speech and OT/PT. I also went outside the school district and got her independent help that our health insurance paid for. I know of one little girl in her elementary school who has the auditory processing disorder part of the SPD disorder, and she's been receiving therapy since she was really little (she's pretty bad).
Like another mom said, make sure you go in with all of your information and insights into your son that point toward him needing to be evaluated. I would start first with your school district, because those services are free. I don't know how easy it is, though, to get a teenager into those services; they like to start kids when they're very young, and I don't know what or how much Special Ed there is at the middle and high school level.
Your son's middle or high school should/might have a Special Education department; you will want to talk to someone there about your son's issues and ask that he be tested for the specific area you're concerned with (auditory processing). They should be willing to do that. Then, depending on whether or not they would work with someone who is already older, I would also put your son's name in at the two places the other posters mentioned here that are near you that can offer help--Fraser's and UW-Psychology department. Perhaps him being older might give him a boost to getting in earlier, since he's already missed so much help that children usually receive earlier in life.
That he's been able to make it this long without help in managing this area of his life is a testament to his resilience and your help, mom. Hopefully he's able to get in for some more help and he'll do well. Does he get frustrated easily? My daughter saw a Childhood Specialist from the age of 5 to 11, which helped enormously with her frustration, anger, and moodiness [well, the moodiness is back, but I blame that on the teenage hormones she's going through now. ;) ].
Good luck. If you have more questions or would like to talk more, contact me. If you're interested, I can also give you the titles of some excellent books to read on SPD.