Techie or Management beyond 39?

relliker writes: So here I am at 39, two contractual possibilities, practically same pay. Caveat? With one I continue being a techie for the foreseeable future, always having to keep myself up-to-date on everything tech and re-inventing myself with every web.x release to stay on top. With the other I'm being offered a chance to get into management, something I also enjoy doing and am seriously considering for the rest of my working life. The issue here is the age of my grey (or gray) matter. Will I still be employable in tech at this age and beyond or should I relinquish the struggle to keep up with progress and take the comfy "old man" management route so that I can stay employable even in my twilight years?
What would slashdot veterans do at this age?