Rename multiple files by pattern in bash with find

Generate 5 files:

$ for i in {1..5}; do touch file_$i; done
$ ls
file_1  file_2  file_3  file_4  file_5

Rename all files starting with "file" by adding .old extension:

$ find . -name 'file*' -exec mv {} {}.old \;
$ ls
file_1.old  file_2.old  file_3.old  file_4.old  file_5.old