People often forget that old tyres are as dangerous as well-worn ones, and it's not something you can inspect visually.
This post from Matt Farah is worth a read. It talks about the real reasons for the death of Paul Walker (re of Fast and Furious fame). Read it
here There's no cut and dried formula either. Some people say 5-6 years, with an absolute limit of 10.
Better to be safe than sorry!
(sorry if the above sounds like a lecture!)
