Well, as we're keeping score, I am also in my mid-40s and have been on 27.
I also use an agent. Through the years, I've had some good ones, one that was not so good, and one who is superb (my current one). As others have said, it's not just about the money. What differentiates the good agents from the not-so-good is the service. I'm not just talking about being an advocate when it comes to pricing, but knowing your likes and dislikes enough to help select the best cruise for you. Being on a cruise that doesn't mesh with your expectations or desires is going to be a waste of money, no matter what method you use to book.