That would be "por los viejos tiempos", if making a toast, or "como en los viejos tiempos" if inviting someone to do something you used to do together long time ago.
Thanks for this, but this is a word for word translation of "for old times" or "like old times". The "for old time sake" (also not sure if it is "for old time's sake") is a special saying/expression in English. I thought there might be a similar thing in Spanish...
