I will try to answer your questions as posed:
1. There is no maximum age to become a pilot. 80 year olds have qualified to be Private Pilots. But over 40 to 45 with a fresh Commercial Licence and no on- the-job experience, I doubt anyone would employ you. Simply because there are plenty of 20 year olds available at that level.
2. You do need some night flying - each country will have its own syllabus. Search via the various licencing websites eg:
www.casa.gov.au for Australia.
3. You won't find it easy to get a pilot job in Australia as an international student. You would be competing against our own young people looking for the same job, and as a former employer of pilots I can tell you that yes, we do favour our own. We are not being racist. I suspect it is the same everywhere else in the world.
4. I will answer this question in reverse. The cheapest place to learn to fly is most probably the USA. Get quotes, but ensure that they will handle the student visa requirements, because the Americans have become quite sensitive about people who want to learn take-offs but not landings.