[TDCruze]

Definitely a gamble but the older the belt gets and the higher the miles the higher the risk of failure. Rubber dries out as it ages. Your belts is now 7-8 years old. Probably could last for another 10k or more miles, but it's also a gamble that you don't want to loose.

 

[TDCruze]

It's not rubber. At least I hope it isn't rubber. I would be genuinely surprised if it were rubber.

I am not a material engineer, but it is some sort of hybrid rubber composition woven with high tinsile cords for strength. Probably much better than old fashioned rubber from a tree, but it still ages and wears out.

Time, heat cycles, number of engine start / stops and revolutions all take a toll. Mileage alone is a very basic estimate of all those things that cause wear. This is done because it is simple to do, to make it easy for the average consumer to know when to change the belt.