Ah, we had a slight disconnect. The KDE *organisation* was formed in 1996, but the Plasma desktop wasn't until 2008, while GNOME's initial release was in 1999.
Discussion
After double checking, the GNOME Project launched in 1997 while KDE was 1996. Plasma released in '08 and GNOME DE was '99, so near enough a decade on KDE, despite KDE being founded first