I really am not sure about the aging ability of Aussie wines. While this is not a Shiraz, I did have a 1997 Clarendon Merlot last year, and it was ok, but well past its prime and it was declining rapidly.
When it comes to wines that can age, I have more confidence in the French, Spanish, American and Portugese wines. There are plenty of wines from each of these regions that can go past 20 years.
As for wines based on the Syrah, the only ones I would trust at this point to go past the 10 year mark are from France.