Old School doesn't work. I think we should use something like Classic Hip Hop which can encompass RUN DMC and Wu Tang, but only the really classic stuff. Aside from that we can call them by numerical generations like Transformers. G1 is Melle Mel, Kool Moe Dee, Cold Crush. G2 is Run DMC, LL, Whodini. G3 is Big Daddy Kane, Kool G, Ice T, EPMD, NWA (Aka the beginning of the Golden Age).

Maybe that works?