What year was the best young rider competition first introduced in Tour de France?

Explanation

The white jersey is one of the jerseys in Tour de France. The best-placed rider under 25 years can wear the white jersey after each stage. The youth competition was introduced in 1975, and has been won by several legendary Tour-winners such as Laurent Fignon (1983), Greg LeMond (1984), Marco Pantani (1994, 1995), Jan Ullrich (1996-1998) and Alberto Contador (2007). There was no white jersey 1989-1999.