Free style competition-can use stroke other than crawl?

I hope to be able to swim at the Nationals at Mount Hood , Oregon. I have been told by several medical professionals that I have an unfixable supraspinitus. Therefore, I cannot swim the crawl stroke. Some questions.1. In freestyle event can a stroke other than crawl be used? 2. I probably would be doing the side stroke, would I be laughed out of the pool? 3. Is there any data about side stroke times that are decent for different lengths? 4. I am 80 years old and it has been a dream to compete in one national , is what I am considering ridiculous? Any and all comments are appreciated. Gil