uncorked red wine

[Noclue]

I have read in some of the posts that most wines are better when they are new. But I have noticed that when I look on a website that sells wine there are some older wines with very good reviews. For example I noticed a Penfolds 1999 Bin 707 Cabernet Sauvignon has a very good review. With this now being 2004 is it still going to be a good wine? It is almost $90 a bottle and I am just using that one as an example. There was another one that I noticed that was a Brookland Valley 1999 Estate Merlot with a rating of 89. again would this be good? How do I know what wines age better then others?