I'm in my mid-30s, grew up tinkering/programming/etc., but I have to admit I just don't get social media. But then I'm not a very sociable person in general. My wife (not a techie), however, is all over facebook/pinterest/twitter/etc. doing God knows what while I'm coding all day.
How I learned of the existence of Pinterest:
Me: "Where did you say you posted that thing?"
Wife (annoyed): "Pinterest"
"Your what?"
"Pinterest"
"WTF is Pinterest?"
"Seriously?!"
edit: Pintrest, Pinterest, eh?