There's nothing wrong with Windows XP. I only recently (early September) went onto Windows 7 Ultimate x64 at home after nearly 6 years with Windows XP. The only reason I updated my OS to begin with was because I bought a new HD.
In terms of gaming, XP x64 is better as it requires less system resources than 7 (as in Crysis which ran on my PC fine under XP x86 now stutters from time to time under Windows 7 x64.
Age isn't a problem, it's security, and features, and to the professional user who doesn't care about fancy aero graphics, or a "I'm too lazy/stupid to know where my programs are installed so I can type in the name and it appears", XP is no worse than Windows 7 if it has the latest patches and security fixes.