Is there such a thing as too old?

[gregdacat]

My tires still have at least half of their warranted tread life left. They are nice and supple with no signs of dry rot. However, the DOT date stamp is 0808 (8th week of 2008) I thought I read once where Porsche recommends replacing tires after 6 years regardless of wear. So should I . . .

a) Replace those bad boys before they blow out at the end of next week,

b) Run them another year and replace them in the Spring of 2015,

c) Or run them until the wear bar(s) show even if it takes another 6 years?