What a load of shit. I'm 25, and I use ebay all the time.
Sure, you can make the argument that Etsy and Amazon are taking business away from eBay. But suggesting that they have replaced eBay as a platform is ridiculous. This is also a very USA-centric view to take. I'm from Australia, so using Amazon is a pain due to manufacturer export restrictions, and the often prohibitively expensive shipping costs. So in many cases eBay is a better alternative. And as for Etsy, it serves a niche. If you want to set up an online store to sell kitschy homemade toot, knock yourself out and use Etsy. But if I want to sell some of my second hand stuff, eBay is what I'm using.