I get this question asked quite a lot. First of all, most wine, even Wendouree is made in a way today that you can drink it quite young. Second, if a wine does not taste well when young, it is highly unlikely it will come around a few years later. Thirdly, you may prefer young wine, its vibrancy and fruit domination. But for those who enjoy mellow characters and more complexity in their wines, this is what works for me.
First class Margaret River Cabernets and Blends should be matured for at least 10 years. They often drink very well at 20 years of age. I would drink the second tier at 7 to 10 years. Coonawarra Cabernet is probably similar, maybe should be drunk a bit earlier. I have less experience with it.
My sweet spot for Shiraz is 7 years. It is usually less tannic and acidic than Cabernet, but at 7 years good Shiraz displays a great blend of primary fruit and secondary characteristics. Some Shiraz comes into its prime later, e.g. Jasper Hill, Giaconda, Wendouree, Brokenwood and other Hunters. I suggest 10 years for these. With Henschke, it depends a lot on the vintage. You should experiment. Penfolds Shiraz is made to last, but improvement beyond 10 years is not so obvious, other than for great Grange years, which I would keep for at least 20 years.
With Grenache you need to capture the fruit. 5 years maturity is often enough. Pinot Noir has changed a lot. 10 years ago, I drank most at 2-3 years of age. Now, I prefer them 5 years old. Good Pinot Noir is still vibrant and fragrant at that time and will go a lot longer.
The white wine stayers are Riesling and Semillon, but they significantly change their character with age. Softness and toffee takes over from citrus. If you like this style, you get the best results from aging these wines at least 7 to 10 years. With leaner Chardonnay being produced these days, you can age good quality wines as well. I drink Leeuwin and Giaconda Chardonnay at 7 years plus, but a number of others could be matured this long as well. However, I often like a Chardonnay fresh.
A lot comes down to personal preferences, but maybe you find my experiences interesting. As an aside, the drinking windows in Jeremy Oliver's wine guide go out too far, in my experience.