Or something like that. I'm not sure exactly what file date/time you're concerned with. Read the help on those commands, look at examples in the help files (Help Get-ChildItem -Full), and consider searching these forums. For example, searching on "AddDays" will probably turn up other people who've been doing similar things.
I have a script that collects the archived logs from all servers and stores them on the network. With the amount we are required to audit, servers' hard drives would fill within a day or two. Any of the logs over 30 days old in network storage are 7zipped. I use the filename for date calculations because we've ended up with new files dated from 1980.