There's no single entity called "Professional School." The term refers to a type of school, not a specific institution with a founding date. Professional schools are institutions that offer training for specific professions, like law, medicine, dentistry, engineering, etc. These schools have been around for centuries, with their origins differing depending on the profession. For example, medical schools have existed for hundreds of years, while business schools are a much more recent development.
To get a more precise answer, you'd need to specify *which* professional school you're interested in.