Remove Documents older than x days in MongoDB

remove_documents_mongodb.js

var date = new Date();
var daysToDeletion = 120;
var deletionDate = new Date(date.setDate(date.getDate() - daysToDeletion));

printjson(deletionDate);

var db = db.getSiblingDB('db')
db.getMongo().setSlaveOk();

printjson(db.messages.find({insertDate : {$lt : deletionDate}}).count());

//delete old Messages:
db.messages.remove({insertDate : {$lt : deletionDate}});

3 years after, this just helped, it took time to understand why $lt was used instead of $gt.
Thanks for this.