From today until the 21st of May, GTA 5 is completely free and if you for some reason don't have it, you should get it. All you need to do is download it from the Epic Games Launcher and it's yours to keep forever.
If it's from years ago, don't even fret. You couldn't predict "Nah, this will def be free". They just dropped the price on the PS4 from about 60 to 15 a few months ago I think.