I am in the process of selling an old classic SL500 Mercedes in tip top condition, and was very surprised when it was pointed out to me, that the tyres were out of date, ( 6 year life span ? )considering they only had approx 1000 miles since fitted at a cost of 1000 pounds ......... this was not a ploy to reduce the price, as his mechanic had done the inspection and all was agreed.
A section from a Kwik fit article I found interesting, especially as this car was mostly under cover.......
Tyre ageing is commonly identified by small cracks, known as crazing, which appear in the tyre sidewall. This is brought about when UV light oxidises the rubber causing it to dry out. While tyres contain anti-oxidising chemicals which significantly slow down the rate of ageing, this wax-like substance is only released when the tyre is in motion. Therefore, if the tyre is not used frequently or is stored away ineffectively, they will age more quickly rendering them unroadworthy when returned to use. Low mileage, older cars tend to be most at risk from premature ageing - as drivers assume the tyres are still in good condition if they have plenty of tread.
More info on dating your tyres etc.
https://www.kwik-fit.com/tyres/information/tyre-age