Perl/Tk is still actively supported, it works, and it might have the shortest learning curve for getting to a point where you can actually have a usable and useful program. Age is not an issue. The Tk library is also supported in other scripting languages besides Perl, so learning to set up a GUI with Tk is a portable skill.
It offers sensible default behaviors so that you can get a decent-enough GUI working without sweating over lots of look-and-feel details, but the default result has an admittedly primitive appearance. The documentation (particularly in the Perl man pages) is amazingly detailed, so when you want to figure out how to tweak things, the information is there (at least, enough so that you can do effective experiments pretty quickly).
There are things it can't really do at all, like bi-directional text (or actually any right-to-left text at all -- I think Arabic is still not possible with Tk), and things that other GUI libraries do much better (there are perl wrapper modules for Gtk and Qt), but Tk's Unicode support is good for all the left-to-right languages, and when you do a standard cpan install of Tk, the test suite that it runs through is impressive. The demo script is pretty awesome too -- very effective for learning how to put code together for various kinds of interfaces.