How old is too old for tires?

[Alien]

I won first place in a car show when I told the judges that everything on my 30-year-old car was original including the tires. They were Michelin MXMs and still performed well at any speed despite their age.

 

[IndyIan]

If the car is driven in the wet, test out the wet grip! If they still stick pretty well, then they are still good IMO. I've tossed bad tires with 1/2 the tread left and only 5-6 years old because I could light up the tires in the wet in 3rd, and 4th gear with my underpowered cars...
If you've got tires that are suspect, do a practice stop, if the they lock and you feel the grip disappear then they are hardened and done. If they lock but still feel like they are helping brake, then they are good.
I don't really care what anyone recommends as its easy enough to test what you've actually got on your car.

 

[BillyHW]

I've never regretted getting new tires. New Tire Day is better than a Birthday.