Any - What is the max safe life for 'space-saver' tyres? - john farrar
I suspect that few people ever change/check these tyres. They just sit there, with very occasional/no use. The risk of a catastrophic failure when they are eventually used must be high, especially as they are not of the most robust construction and are inflated to 60psi, however I have read of no such failure(s).

Maybe they are better than they look, or perhaps being stored in the dark extends their life to say 10-15 years? Seems unlikely to me.
Any - What is the max safe life for 'space-saver' tyres? - unthrottled

They'll age just like a conventional spare tyre. Heat, oxidation and UV embrittles the rubber. Sitting down in the well, none of these should be as high as a tyre in normal use.

People can't get past the 'pram wheel' mentality of space savers and try to contrive safety arguments against them.

Given the size of modern car tyres, a full size spare often can't be justified in terms of real estate.

Any - What is the max safe life for 'space-saver' tyres? - jc2

Very few modern cars have true "spacesavers"-most use a conventional tyre but of less width and same rolling radius.They will age like any other tyre.

Any - What is the max safe life for 'space-saver' tyres? - Armitage Shanks {p}

Not really - as unthrottled says, no exposure to UV for a start

Any - What is the max safe life for 'space-saver' tyres? - jc2

Many spares are carried outside of the car-alright-underneath!!Some,even,in the engine compartment.