Tubes do age, but it's slow enough not to make a difference. I've noticed that over time they become less elastic and a bit more brittle. It's never enough to cause a problem in itself, but I've noticed that older tubes sometimes split or tear when newer tubes would only puncture.
I've also had older tubes tear apart when removing them from flatted tires.
I wouldn't scrap a tube over an age issue, but if going on an extend trip might carry one more spare than I otherwise might.
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