Sometimes, when working on a new machine or a machine with a screwy clock or incorrect TZ you can then have files modified in the future which breaks some things.
To find the files modified in the future use
find ./ -type f -newermt "1 days"
Now to fix the files to NOW use
find ./ -type f -newermt "5 days"|xargs touch
You can use -d with touch to specify the date you want to use instead of now.
How about finding all files that have not been modified for more than 20 years?
find ./ -type f -mtime +7300
The +7300 is 20*365 or 20 years. If you wanted to delete these files then -delete will do it. If you wanted to archive these files then output the filenames to a file with > filename.txt and then either sed that into cp commands or feed it into the cp.