Permanently prune backups created by Time Machine I am cleaning up old Time Machine backups, which slows stuff down to a grind.  I want to tell Time Machine to delete all backups older than 3 months.  I'd also like for Time Machine to keep that as a default rather than having to do that by hand myself each time.  How do I do that?
I was able to find this app, but I've never used it, I don't know if it works:
Time Machine Editor

It purports to edit the frequency rules .plist for you. 

Otherwise:


These are the rules. If you don't like them, use a different backup solution.