Did you see old mate? He was heaps drunk last night!
Apparently you can use this term to refer to anything. Especially if you want to avoid speaking someone's name (and it is shorter than "He who shall not be named") or you've just plain forgotten.
I think this is a fabulous way of masking your inability to remember the names or people, and it also works for places and things. As in:
Grab that old mate while you're at it
Why remember the word for "box" when you can just throw "old mate" at the problem?
The word "mate" has sexual connotations where I'm from. It can be used as a verb when speaking about animals expressing their love. As a noun I always used it as a reference to significant others in a clinical way. As in "high maintenance women are good mates for wall street finance hotshots". But in Australia they say "partner" instead since mate is so heavily used in the brotherly-love kind of way.
I ran into a guy at a party that was complaining that there is no good word in the English language for a person who is not your "wife" but is your "long term girlfriend". The term "partner" lacks a gender so in the US that usually implies same-sex relationships. Perhaps we need a new word, or maybe we can just use "old mate"!