Alex, you've been here 2 minutes and already asking the hard questions!
You are just embarking on the journey to find out which wines you like and the challenge of picking young wines that will cellar well and/or drink well while young.
I haven't tried the 2003 Black Label yet, I have a bottle to try, but young Coonawarra cabernets with cellaring prospects can be a little daunting when released. Sometimes a vigorous decant a few hours before drinking helps, sometimes not. In cabernets there are "good" green characters such as mint, touches of green leaf or grean bean, as long as there is also some nice ripe berry/blackcurrant fruit, but anything too much like a lot of green capsicum, too much herbaceousness or hard unripe green characters are not a good sign as they will often stay with the wine or dominate it as it matures.
The key thing the "experts" look for in young wines that have long cellaring prospects are the adequacy and quality of the fruit, oak, tannins, acid, the alcohol level and the balance of all the components. If a wine is inherently balanced (no one component has too much dominance) it should be reasonably drinkable when young, especially if (like me) you don't mind fairly aggressive tannins and a bit of oak.
With your example of the 2002 Bin 707 Cabernet, I would happily drink that now, I think it tastes fine and has good balance, but having some experience with 707 I know it will be much more enjoyable in 10 or 15 years time. It's also not great value at $100+. Most of the wines I buy to cellar are attractive enough to drink on release, I don't buy wines that I couldn't drink young, sometimes you may only want a glass or two though if they are big wines or pair with a chunk of rare beef to cut the tannins.
Some writers score based on "what's currently in the glass", others, including I think JO, also use their experience to score a wine on potential as well and allocate a drinking window based on their perception of when it will taste best.
Unfortunately it's a matter of trial and error to find which writer(s) you agree with and over time as you palate develops your taste preferences may change, so don't buy up too big on the first big pay packet after you graduate. I find myself agreeing quite often with JO on his ratings and his drinking windows are often spot-on for my palate preferences, although I tend to take a year or two off the longer ones.
To be fair, take some of my comments with a grain of salt, my palate doesn't suit a lot of people, for example I'm happy to scoff a young 2002 Durif from Warrabilla (over 17%a/v) with authentic Thai food, it is a brilliant pairing, as are many shiraz that don't have too much oak or tannin, such as a lot of the better Barossa Shiraz.
Stick at it, it's worth the effort. And when you have Shiraz, Cabernet and a few other varieties sussed out, you can start the search for a decent Pinot that you can still afford, that should be good for a few frustrating years.
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