By Piya Sinha-Roy LOS ANGELES (Reuters) - Rock group Kings of Leon are getting less serious with age, as the band prepares to bring "young and fun" new music on Friday to their fans across the world in a quirky collaboration with comedian Fred Armisen. Kings of Leon, formed by Followill brothers Caleb, Nathan, Jared and cousin Matthew, are marking a decade in the music industry since their debut album "Youth & Young Manhood" was released in 2003. After a hiatus in 2012, Kings of Leon are back on the road to support their upcoming sixth studio album "Mechanical Bull," due out in September. ...