I'm 36 and have had terrible rounded, hunched shoulders that I've had since adolescence. Last year, I bought a DVD on Amazon called "Posture, Get It Straight!" by a woman named Janice Novak that has really good posture exercises on it. When I do the DVD consistently, I see results, but, of course, it's sometimes hard to fit it in on top of my regular workouts.
The DVD also comes with a free latex band to do the exercises with. Many of the exercises are regular strength-training ones that you'll find on Cathe's DVD's, but this DVD also goes over correct posture, etc. I've found it to be really helpful for getting me to focus on my alignment.
Hope this helps!
LeanneM