It's 18 years old in 2012. Riverdance started as the interval act of the 1994 Eurvision song contest. You can see that original performance, which was just 7 minutes long, at the link below.
On notes from 1928 to 1976, Lady Lavery featured on the £20 note. On notes from 1980 to 1992, William Butler Yeats featured on the £20 note. (The 1976 notes remained in circulation until this...