I'm 31, and I have coworkers in their late 30s and early 40s, working in a large multinational with legacy systems.
The truth is, while it doesn't get that much mentally harder to learn new technologies, it is very hard psychologically.
For someone used to a large paycheck, to being the go-to guy in the technology and set in their 9-to-5 ways, to get out of their comfort zone, and admit that what they know is no longer relevant is scary as hell, especially for those with families.
So, rather than update themselves and make up all that lost ground from getting too comfortable, they'll try to keep in place the old legacy systems only they can maintain.
I got caught in that trap too, one of my main responsibilities is maintaining a Forte 4GL system ( http://en.wikipedia.org/wiki/Forte_4GL ).
While I've kept myself relatively up to date, it was on Microsoft .NET technology only, and I'm still a few years behind. I wanted to supplement my income, and took a look at the online marketplace, and it confirmed what Hacker News was already showing me: my skills are useless, I don't know Ruby, Javascript, the open source stacks, Amazon Web Services or anything currently relevant and in demand.
I can either try to switch into management, or accept I'm obsolete and take a large pay cut (or try to improve myself on the side, probably by trying to do a startup) if I want to stay relevant.