There is certainly a tyre industry recommendation that tyres should be replaced by 7 years from manufacture date - they do deteriorate with time due to UV light degradation and oxidation.

I'm not aware of any specific law or regulation on maximum age - just those relating to condition.

Although they don't all do it, caravanners are advised to have new tyres every 5 years despite little tread wear - this ensures that any time in the supply chain is taken into account.

But if the car was kept in the garage, UV is a non issue. There's still the issue of oxidation i suppose.

Oxidation is the process - it is accelerated by UV, or sunlight as we usually call it. I have a 23-year-old car with a full set of tyres of the same age. They spent their early years in storage, and I understand have been 'show wheels' so are very little worn. In my ownership they have passed four MoTs without comment or advice from the tester, who I trust implicitly.

Quite a few older cars will have an unused spare tyre which should be roadworthy for the same reason - kept in dark/shade and not baked in sunlight.