As per Edmunds: Carmakers such as Nissan and Mercedes-Benz tell consumers to replace tires six years after their production date, regardless of tread life. Tire manufacturers such as Continental and Michelin say a tire can last up to 10 years, provided you get annual tire inspections after the fifth year.
I just bought my 4 track tires from Tire Rack; the rears were 3 months old and the fronts were about 1.5 years old.