Good rule to have. I've been disappointed by some older wines that haven't developed well (2009 Mitchell Sevenhill cab is a recent VM example) so I tend to be careful too. For the Mitchell, the review (91 points) was on the fence and the wine didn't go the way it might:
"Good retention of purple-crimson hue; the bouquet is fragrant, and like the fore-palate, has clear and attractive cassis and redcurrant fruit; after a mid-palate dip, savoury tannins come through strongly on the finish, needing to soften. The question is will they do so before the fruit fades?"
The 2008 Umamu cab merlot was a buy for me based on a good score (91) but a review that was positive about its ageing prospects, and I've been very happy with the couple of bottle I've opened:
"Strong purple-red; an intense, penetrating blend that pulls no punches; despite its power, the black fruit and briar characters are well balanced with each other and with the tannins; simply needs time"
Thanks Roshea and Tanark2. In the end, i ordered the last 11 bottles of the 2008 and topped up with 9 of the 2009 to get the free shipping. Cracka obliged to give me the $12.99 rate for all.