YouTube offers hundreds of movies, some of which were made in the 1950s, for free and legal streaming. It also makes available paid rentals of many copyrighted movies, some of which are also from the 1950s.
Some old movies are available for free distribution and viewing because they have fallen out of copyright. YouTube features many of these for free viewing.
Many movies that are still under copyright, some from the 1950s, are also featured on YouTube for legal streaming, but it is usually necessary to pay rental fees in order to watch these so the copyright holders can be appropriately paid.