The first US type Certificate for an airplane was issued in 1927. Before that US aircraft had no certification. Homebuilt and kit built aircraft were very active until the 1930's. At some point in the thirties homebuilt aircraft were in theory grounded except in Oregon where the state allowed them to fly. In reality people like Bernard Pietenpol continued to fly. There were also a few airplanes certified in Experimental sub categories with racing and research and development being two examples.
I think most people today believe EAB came about because of EAA. EAB rules were first published in Oct 1952, three months before EAA was formed.
The EAB rules came from efforts by the Oregon Group.
The EAB rules did not provide for passenger carrying. EAA discussed seeking passenger carrying approval but little was accomplished.
In Oshkosh Steve Wittman gained certification of his Wittman Tailwind in Jan 1953. In Dec 1953 Steve performed load test and dive test with the CAA observing. The Tailwind became the first EAB aircraft certified to carry a passenger. (Not for hire)