Kent Rasmussen has long stated that PS has the ability to age superbly, due to its tannins, and will pick up after 15 years and have another, very complex drinking period that will last at least until it's 25th birthday. Most people with whom I've raised this theory, many of whom are very knowledgeable about wine in general, dismissed this theory as lunacy.
I'd like it to be true the vast majority of the time. But apparently, it's certainly true for some PS. I love to get confirmation of my pet theories (pun intended).
(N.B. -- I am really sorry about the lack of posts. Work has been eating me up lately, and in fact, I shouldn't even be posting this)