There are a number of dubious theories about Columbus' origin, but we have a smoking gun: a 1470 Genoese court document which notes the unpaid debt of a young Christoforo Colombo to a fellow Genoese citizen. In his will, Christopher Columbus mentioned this debt.

There are several other official documents from Genoa which mention Columbus long before he rose to fame.

I would advise caution. Tourist guides are not always the more reliable sources, and then we have to add politics.

I know this goes beyond the 20-year rule, but I think it's important to understand this issue: the rise of separatism in Catalonia and the need to find local figures of relevance, wherever they might be found.

It's just not Columbus, but even Cervantes has been claimed as a Catalan, to the point they say that Don Quixote is "is a rough translation into Spanish of a work which was originally written in Catalan." http://www.businessinsider.com/afp-cervantes-and-columbus-swept-up-in-catalan-separatist-push-2015-9

I've asked similar questions in the past, without much luck. In particular, I'd like to know what people here make of the claims by David Sarfaty and others that Columbus made Catalan-influenced errors when writing in Spanish and gave distinctly Catalan names to many of the places he discovered. I don't know enough about late medieval Romance languages to tell whether these claims hold water or not.

Another piece of evidence Catalans use is that his writing show all the linguistic clues that he was a Catalan speaker. https://books.google.it/books?id=TggNAQAAMAAJ&dq=&hl=en

There are even experts in Barcelona who can identify his former home.