If I hear that Millennials are "social media experts" one more time, I think I may explode. I've given dozens of social media briefings to all generations and have spoken to dozens of other people who have done the same and the conclusion is always the same - the ages of the people in the room are irrelevant when discussing social media knowledge/experience. I've talked with rooms full of SES's and other senior leaders and when asked how many of them are using Twitter or are blogging, about 10% raise their hands (everyone uses Facebook). I've also spoken with a LOT of college students and recent grads and the % is about the same.
This stereotype unfairly raises the expectations for your new hires because they're supposed to know all of this "kid stuff" and lets the Gen Xers off the hook because we reinforce this stereotype.