You can use find to do this, provided that you know the number of days before which you want files deleted, using the -mtime +<No. of days> option, for example, to delete those files last modified more than 30 days ago:
find /<path to files> -mtime +30 -exec rm {} \;
Note that it is good practice to issue a -print command before executing the rm option, just to make sure that you're picking up only the files you want to delete and no others:
find /<path to files> -mtime +30 -print
Hope this helps.