I am a man with longer hair(long enough in front to touch chin, back is so the top of shoulders) interviewing for a job in the medical field. At my current job I just pull my hair back and into a very small tight, rolled up ponytail. Do you see the doctor's office not hiring me as a result of this?

The medical profession is pretty conservative. I have nothing against long hair, used to have it myself, but it could be a problem. You don't need to get a buzzcut, a traditional businessman/politician style haircut should be fine. Traditional haircuts like to kind on retro TV shows like Mad Men have been making a comeback lately.

There is no rule, and no law about it. But assuming you will have dozens of others trying for the same job, you need to look into the culture of the office or facility you want to work for. But yes the long hair will make it harder to find a job in that industry.

I think that people are a little more enlightened now. IMO if you appear neat, clean and present yourself well you have just as much of a chance of getting the job as anyone else.