Sheel Script for Deleting files older than some days

find is the common tool for this kind of task :

find ./target_dir ! -name 'stayhere.txt' -mtime +5 -type f -delete


EXPLANATIONS

./target_dir your directory (replace with your own)
! -name File to exclude
-mtime +5 older than 5 days
-type f only files
-delete no surprise. Remove it to test your find filter before executing the whole command
And take care that ./target_dir exists to avoid bad surprises !