I'm a 40-year-old developer, and it's become apparent that my .NET skillset is woefully out of date after five years of doing various bits of support.
I'm sorry. Honestly, I really am sorry. I don't like that framework, I don't like that language. Also when I was growing up it was largely a "pay to play" realm and largely still is (although I know I can get my hands on an express IDE).
This really is less than helpful, albeit typical for the longer-run members in this community. It's .NET, pay-to-play, and therefore irrelevant. That, in truth, is political garbage.
To answer more fully - age is irrelevant. If you desire to pick up the variations between .NET 2.0 and 4.0, just put in the time necessary to practice some of the newer things. You could also pick up C#, though it isn't absolutely necessary, because the positions open on the market lean more heavily toward C# than VB.NET. It's primarily syntactical sugar, you'll find, but some of the newer things are performed a little more easily in C# than VB. Some of the more exciting aspects of .NET lie in the direction of F#, too, which is pretty easy to experiment with (and fully supported by Mono/Monodevelop).