I'm 16 (almost 17) and started rocking Starcraft a little bit after it came out(I was what, ~11? ), I had played Doom 1&2 a little bit, but I got serious into it for Starcraft.
I was running a Ti4200 with an Athlon 64 2800+ and 512mb of crap Ram before I got my 6800GT & Gb of Kingston and I could run HL2 at 1280X1024 at High Settings. So my vote is for teh Cpu.