You should look for modified time and not acccessed time, because on WIndows, it is difficult to copy a file without changing the access time. So, you may want to look for modifying your script to look for modified time and delete the files which have not been modified. Also, if this is Backup Exec 2010, you may want to check BE Archiving option, which can help you archive old files, based on various rules you specify in Backup Exec.
Please mark it a solution, if this is useful.
Thanks