I am a bit late and you seem to have made the decision already...here a my 2 cents...
IMO...10 years old is generally too long, but it would be a case by case scenario. If there is cracking on the sidewall, this would generally mean that it is time to replace the tires. Often called weather checking and caused by the reaction between ozone in the air and the rubber of the tires. You dont often see this as usually tires wear out long before it has a chance.
Heat is the enemy of tires and there is nothing harsher than a long road trip to the US. It would be a sour note to have a tire failure on a nice holiday. Good way to ruin things.
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