A reason to feel old

The film version of Mamma Mia has been released (the stage version was great). All the reviews I have read note a scene involving the ABBA song "Dancing Queen."

And then it hit me. The Dancing Queen is "only 17". That song was recorded in 1975 and was a big hit in 1976 (when I was 9). Which means that the Dancing Queen is now pushing 50.