What would a hipster look like in the 19th century?

Can you explain what you mean by "hipster" in this context? There are a few different ways I could interpret this - hipsters as counter-culture, hipsters as wealthy young people, hipsters as people with exaggerated dress ... ?

Was the concept of Retro around then, making older clothing cooler?

Yes and no. The idea of wearing actual 20+ year old unaltered clothes or accurate reproductions (as in the modern vintage subculture) was essentially unknown until the later 20th century. However, historicism has been a huge part of fashion since the late 18th century, as I described in this older comment.