Sharpest Tongue in the West
Yes, tyres do deteriorate with age, although 4 years should be fine if you use it regularly. All tyres are dated with a week and year of manufacture, denoted by a 4 figure number on the tyre wall. So 0111 would be 1st week of 2011.
6 years is about what most would use as a benchmark age to start looking at replacing them, and something to know is that you're more likely to prolong the life of your tyre if you use the car regularly. A sign of a tyre suffering from age is cracking/crazing around the tyre wall.
Porsche Cayman S |Jeep Grand Cherokee|1988 Ford Fiesta XR2