Time named Shawn Mendes one of the 25 Most Influential Teens of 2014 (along with Nobel Peace Prize winner Malala Yousafzai). Last July, the then-15-year-old became the youngest artist to debut in the Billboard Hot 100's top 25 with a first chart entry. (His acoustic ballad “Life of the Party” entered and peaked at No. 24.) Earlier in 2014, the former youth hockey player sold out a headlining date at Los Angeles' 5,900-seat Greek Theatre in less than an hour, which might explain why Taylor Swift hand-picked him to open 20 stadium dates during her North American 1989 tour this summer.