Shawn Mendes scores a first in the 56-year history of Billboard's Adult Contemporary chart, achieving the unprecedented feat of tallying three No. 1 songs before age 20. Mendes, who celebrated his 19th birthday Aug. 8, earns the honor as "There's Nothing Holdin' Me Back" rises 2-1 on the chart dated Nov. 18. The song follows his debut AC entry "Stitches," which led for two weeks beginning April 30, 2016, and "Treat You Better," which reigned for two weeks beginning Feb. 11. The Adult Contemporary chart measures total weekly plays, as tabulated by Nielsen Music, among its reporting panel of 84 AC radio stations.