FAA Part 103 for Ultralights was adopted July 30, 1982 and effective on October 4 that same year. Federal Aviation Regulation Part 103 formally established what truly is recreational flight.
ABOUT PART 103 FOR ULTRALIGHTS
Part 103 established limits on size, performance, and configuration and also established that people flying them needed no certificate or medical qualification.
Link: FAA Part 103 for Ultralights downloadable .pdf.