You are confusing the term "straight razor" with razors just in general. "Straight razors" are specifically long single-edged razors that completely fold into a handle. In the modern world, the term is used loosely to differentiate a naked single-edged blade from the ubiquitous safety razor. The razor as a basic technology—that is, a very sharp blade intended for removing hair from the body—is millennia old. They were not using stone blades to shave in the 16th century CE. Here is an example from Roman times. The Romans manufactured high-quality steel blades and were familiar with virtually every shape of blade known today, including precision surgical instruments. Here is a slightly earlier example from the early Celtic site at Halstatt which is very well preserved thanks to that wonderful Alpine anaerobic environment. Here is an example from the Egyptian Bronze age, and another.