One avenue worth thinking about are the emergency services (Police, Fire, Ambulance). They are all (very) underpaid for the work they do however this is offset by the excellent rosters (particularly the ambos and firies) which allow another job on the side. It is very satisfying and you're working with a fantastic bunch of people.
There is no upper age limit however the selection process for each service is very competitive and takes a number of months to go through.