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?" "Pint…
Part of that is just gender. Pinterest is aimed almost exclusively at women. You haven't heard of it because you're a dude and it's not marketed to you or your friends. Hell, I'm enough of a tomboy that I don't really use it. I looked at it a year and a half ago when I first started transitioning to female because I heard that girls are supposed to like it, and I never got into it because it was all about fashion and…
The obvious use case is wedding planning. One board each for dresses, rings, locations, cakes, table decorations, invites, etc etc. or for redecorating a room - it's brilliant for that kind of stuff.
(I say brilliant, and I'm a Pinterest fan but the site has some user-hostile behaviours on mobile so I ise it a lot less often than I used to.