penchef

#!/usr/local/bin/bash

# source: https://stackoverflow.com/a/51374983

git for-each-ref --sort=committerdate refs/ --format='%(committerdate:raw) %(refname:short)' | \
  awk "\$1 < $(date -d "-100 day" "+%s") {print(\$3)}" | \
  xargs git branch -D