It's natural for people to gain a little weight and size as they grow older. In fact, it's healthy to do so. Tamilee Webb (another exercise guru) used to be a little string bean, but now she's filled out all over her body. She's still in great shape, but she's got more "curves" now. I would say her waist is about 50% bigger, but her abs are in great shape.
I agree with the person who said that you might not be able to drop that 5 pounds because your body needs it. If you're in good shape, then don't worry about your waist size. Ya gotta live with the body you gots. Your body just might be a size 6 instead of a size 4, that's all. To push into a size 4 might be too much to ask.
Okay, but if you really want to get into those size 4's...
Stop doing ab work. Ab work builds up the muscle in the stomach region, pushing your abdomen outward. For example, check out Cathe's abs. She's got a flat tummy, but her abs have built out her abdominal region a little bit. She could probably lose an inch or two around her waist if she completely stopped doing ab work, causing her ab muscles to shrink in size...but I think she looks great just as she is (you probably look great, too, by the way
). But I know where you're coming from -- when I used to body build, my biggest complaint was that the gym-style oblique work I was doing was making my waist wider, and my pants tighter. My training partner told me to stop doing so much ab work if I wanted my waist to shrink. I did...and my waist got smaller.
Hope that helps.