My husband and I are both over 45 and are here on a 457 visa. We didn't have any problems with our age (it didn't even come up as an issue.) The key, obviously, will be finding a company that is willing to sponsor you. Some thoughts: Are you working now? If so, will your company sponsor you to come here and work? does your current company have any affiliates or customers in Australia that might sponsor you?
What kind of work do you do? Start googling companies in Australia that are in that type of business - larger companies often post career opportunities on their website.
Good Luck.