And Larry didn't mention - only in a straight line, no corners, no bumps, and no fancy stuff like accelerating or slowing down
I wouldn't run 'em, but I have a buddy that bought an '84 deLorean with original tires back in 2006 with 18,000km on them (wow, 22 year old rubber, but hardly broken in), he drove on them until last year but only to local shows and never on the highway with a passenger in the car. Fear and common sense finally overcame the pride that comes with 'originality'.
... I believe the D.O.T. recommendation is replace tires after 6 years of use (if the treadwear doesn't do them in first), and don't use them if they're older than 10 - visual inspection won't necessarily show deterioration that could be happening within the tire and between the rubber and the steel belts.