If I open finder and recents I see there by default, there are 3 years old documents in this recent folder, although I have made more than 30 voice recordings recently in dec 2020. I only see one of them there. Why is that? Doesn't recent mean recent..? How can I see in my recent folder just recent files.. ?

There are several places Recent files are found -- application File menus, Finder Go menu, Apple menu, etc. Since you said Finder I'll assume the latter two are what you're talking about [it would help if you were more specific].. Apple menu > Recent Items and [Finder] Go menu > Recent Folders both have a Clear Menu command at the bottom of the menu -- in theory that should clear out older "recent" files, though apparently it may not always work as intended. In System Preferences > General you can turn off Recent items [set to None], and you can add certain folders to the Privacy tab in System Preferences > Spotlight, but then you won't see any new recent files [and the Spotlight method may impact your ability to do searches]. Recent item lists have always been a little flaky, I wouldn't depend on them too much -- you could instead create aliases to locations you use frequently, for quick access..