They don’t check your I.D. in the big leagues. Kyle Muller is vying to become the next youthful starter to grace the Braves’ ensemble. Mike Soroka, Touki Toussaint, Kolby Allard, Kyle Wright and Bryse Wilson, among others, already have tasted the majors. Muller, who turned 21 last month, certainly looks the part: The hard-throwing, Texas-born lefty stands at 6-foot-6, 225 pounds.