Millennials know who Snowden is because they watch the Daily Show.
The real difference is that older people are more likely to be fearful of whatever boogey man du jour the government is pushing. When I was a little kid, my grandparents really were afraid of communists. When I was a teenager, I was told by older folks what horrible stuff marajuana was, and how it would definitely ruin your life. In 2002 I was having a discussion with an older co-worker, who was a really smart guy, and he told me that he was concerned and scared about Sadam Hussein having weapons of mass destruction.
Today government officials tell us we are supposed to be afraid of terrorists, and that Snowden hurt their ability to fight these ubiquitous terrorists.
I do not know why, but as people age, they watch more TV, become more fearful about the state of the world, and buy the official propaganda. I'm am trying to avoid this.