I always like to point out the telegraph relay computer[0] built by one Harry Porter. I think that pretty much takes the cake for retro hardware. It also brings up the question of how early a binary computer could have been built, since the relay was invented in the early/mid 1800s[1] and Boolean logic in 1847[2]
[0] https://www.youtube.com/watch?v=n3wPBcmSb2U [1] https://en.wikipedia.org/wiki/Relay#History [2] https://en.wikipedia.org/wiki/George_Boole#Symbolic_logic