My wife and I have just started eating primal. I'm in my mid-thirties, 5'11" and 160 lbs., and I've never really had to work to maintain that weight. I'm starting because my skin has been bad since the 80s, my energy has been really low, and two of my brothers report feeling much more energetic since going primal. For me, it isn't a huge step; I naturally prefer fat/salt/protein over carbs.
My wife is on board, and for her it's a much tougher step. She has a sweet tooth, and today was her first day eating primal. Here's the cool thing: when I got home from work, she said "it's weird, I haven't been hungry all day."