Mass close existing topics older than x?

[Tealk]

@Discourse

Close all topics created before a specified date (includes post action)

Topic.where(closed: false).where("created_at < '2015-01-01'").find_each do |topic| 
  topic.update_status('closed', true, Discourse.system_user)
end

Yes, there would be something similar linked, how can I narrow it down to one category?