Cartridge life really only 3 years??

Hi. I am a long-time audiophile, but have just re-discovered vinyl after thirty years. Wow. What a difference equipment can make! I bought a nice turntable with very low hours on the cartridge. It is a MC cartridge. A local trusted audio dealer (who does not sell cartridges, by the way) told me that I should change the cartridge to get the most out of the sound, as cartridges lose their performance after about 3 years, whether used or not. True???