My age scale for PC's (for Year 2016) :
Cutting Edge - Anything with AVX support (Skylake is Bleeding Edge 😀)
Modern PC's (Nehalem/Phenom and newer without AVX),
Classic PC's (Core 2 Duo/AM2 and newer),
Retro PC's (All Pentium 4's and D's with Socket 939/754 + Socket 370/Socket A),
Vintage PC's (older than Pentium III and Athlon XP).
Core 2 Duo's (and Core 2 Quad's) are in second group (Classic), because they can run any OS or game U can throw at them.
Socket 939 is "dead" for over 10 years (last CPU was introduced for it in January 2006), so I think that should be concidered Retro.
Newest Windows for S939 :
1) Win 7 x64 SP1
2) Win 8 x64 or Win 8.1/10 x86 (64-bit versions of Win 8.1 and 10 are not supported natively on Socket 939 CPU's).
I think Core 2 Duo PC's (typical Windows 7 era PC), don't become "Retro" anytime soon (still - Conroe's 10 year anniversary is in June 2016 😀).