The -mtime option can be used to return files and directories that were modified x or more days ago. For example, to return files and directories that were modified 14 or more days ago below the tmp directory.

find /tmp -mtime +14

For example, to return files and directories that were not modified 14 or more days ago below the tmp directory.

find /tmp ! -mtime +14

• The -atime option can be used to return files and directories that were accessed x or more days ago.
• The -ctime option can be used to return files and directories that were changed x or more days ago.

To include the date and time the file was last modified in the output.

• %y = time last modified
• %n = file name

find /tmp -exec stat --format  "%y %n" "{}" \;

This will return something like this.

2020-07-06 05:50:18.594805437 -0500 /tmp/foo.txt
2020-07-06 02:10:38.898884577 -0500 /tmp/bar.txt