You can use the "find" command.
The "find" command finds files based on many different criteria specified on the command line.
This example will only find and print the full path of files older than 15 days on the entire filesystem:
find /* -mtime +15 -print
You can also cd to another directory and find will search starting from that directory
cd /another/directory
find . -mtime +15 -print
also this will do the same:
find /another/directory/* -mtime +15 -print
The find command can also execte another command on each file found, for exmple
find /another/directory/* -mtime +15 -exec rm {} \;
Will delete all matching files.
BE VERY CAREFULL WHEN TESTING THE -exec ARGUMENT SPECIALLY WHEN USING "rm"