I have some 1st edition books and I'm uncertain how old they have to be to be called antiques. Anyone familiar with antique books?

I have a number of hardback cover antique books from my father's collection that I want to carefully clean and preserve. The books are in excellent condition.

I have a huge library of vintage books I inheret and I need to sell them online .All are in spanish and are antique. The oldest one is from 1600s.I have also many from 1900s until the 60s.The themes are children,poetry,biography,novel,enciclopedia and others.

I have a collection (about 75 books) of school books, mostly Shakespere plays, and Longfellow's poems, that are all from 1901-1925. Any guesses on how much they would be worth? (Please list a scource) They are all in great condition. They aren't signed. Not sure where that came from..... They were my grandmother's.