Climbing stairs is injurious to knee?

I am a 38 YO man, 5'8", 60 KGs. Here is my question.. I always take the stairs instead of an elevator if less than 5-6 floors. I always take two steps at a time easily, and almost always reach much before the elevator in which my wife & kid go. At least 3-4 times daily, and i feel good about not getting out of breath. But recently someone advised me in strong words that too much of climbing stairs will wear off the knee cap and prove injurious in the longer term. I am a bit confused. Is it true? Should I limit stairs climbing? If so, what is the ideal rate? Thanks a lot.