You should not delete all changes older than 30 days (I think it’s somehow possible exploiting Git, but really not recommended).
You can call git gc --aggressive --prune
, which will perform garbage collection in your repository and prune old objects. Do you have a lot of binary files (archives, images, executables) which change often? Those usually lead to huge .git
folders (remember, Git stores snapshots for each revision and binary files compress badly)