I'm pretty sure the first time I heard this, it was from an early-twenty-something woman in the office I worked at, which would have put it around 1999, actually. (I said 1997 before, but I think it had to be 1999-2000.) I thought it was weird, but it caught on and hasn't gone away. It's mostly a female thing. It has morphed into just "Right?" in the last few years. As in: "I love
Breaking Bad." "Right? So good!" Or: "That guy is really tall." "Right?" And so on.
It might go away, but it's been around for more than a decade in SoCal, so I wouldn't hold my breath.