Re: Pain in left knee after hitting balls at the range.If your knee is hurting, that's your body telling you something is wrong. So when you start to feel pain, quit hitting balls. Perhaps chip or putt or something less stressful. Maybe your knee is just a little work and can get stronger. Also, take your time when hitting balls. Go through your pre-shot routine of lining up your shot, etc. Don't wear yourself out just machine gunning balls out there (like I used to do at your age).
Most likely you're just at that age where your body is growing a lot and the pain is probably something minor. I don't think it's worth changing your whole swing over. Just don't take it easy and it'll probably go away with time.
If this is a REAL pain to the point where it hurts to walk, you need to see a doctor.