I am constantly pestered by recruiters and companies to interview. I think one of the things that helps is that I trimmed my resume to omit material older than 5 years, removed unnecessary dates, and I make a point of drawing attention to studying for new industry certifications. It probably doesn't hurt that I stay physically fit, either. As cruel as it may be, if you're out of shape and look "frumpy" or "run down," that will count against you far, far worse than your age.
The key is to make the age factor irrelevant by not drawing unnecessary attention to it or by projecting a stereotypical "middle aged" image. We can argue all day about whether that's fair or not (it's not), but you have to do what you have to do.