You are just under 5 years old (2401 = June, 2001) and as Bernie says, you are at the point where you should start planning for replacement in about one year. Mine are 5001's and I have no qualms at all about using them another year and traveling cross-country with them. But by next year at this time they will be getting marginal and I will most likely replace them before attempting any summer travel. Hot weather is tough on tires.
You probably have plenty of tread left, but take a quick look at each tire to be sure. If one or more of the tires has been run out of balance or out of alignment, the wear may be uneven. If there are any tires in poor condition or worn badly in one place (e.g. along one edge), consider replacing those now to be on the safe side. One technique is to put two new tires on the front wheels and the best 4 of the 6 older ones on the rear. This gives you good tires to steer with and also spreads the tire expense over a longer time period.
