find . -maxdepth 1 -type f -mtime +5 -exec rm {} \;
mtime stands for ModifiedTime. Values above zero means older than, below zero means less than. Ex. +5 means older than 5 days. To remove everything modified the last 24 hours but keep 1 day or older use -1
If you want progress bar this becomes:
find . -maxdepth 1 -type f -mtime +5 | pv -l -s $(find . -maxdepth 1 -type f -mtime +5 | wc -l) | xargs rm