If 50 years equals "historic" and 25 years equals "antique," then how many years equals "retro"?

So, Fiona Apple's "Criminal"--one of my all-time favorite songs from high school--was playing on 106.5 this afternoon. I was all excited until it ended and some caller won a prize for being able to "name that retro replay." What?! I guess I can expect to hear it on some oldies station any day now...