Sage's career began in 2011, when she got the part of Grace on How to Rock, which first aired on February 4, 2012. She appeared as Brianna in the 2012 teen drama The First Time. Sage has also guest starred on Nickelodeon's Victorious and Bucket & Skinner's Epic Adventures. In 2013, she appeared in The Bling Ring alongside Emma Watson, Grown Ups 2 alongside Adam Sandler and Chris Rock, and Poker Night with Beau Mirchoff and Ron Perlman. In March 2013, Sage was cast in the pilot/thriller by Rand Ravich, Crisis, for NBC. She had a role in the 2014 film Neighbors, with Seth Rogen and Zac Efron; she played the part of Efron's girlfriend Brooke Shy. Sage was a nominee for the MTV Movie Award "Best Kiss" for her onscreen kiss with Rose Byrne in Neighbors.
　　She played Lacey Pemberton in the 2015 film Paper Towns alongside Nat Wolff and Cara Delevingne. The film is based on the 2008 novel of the same name by John Green.
　　Sage is set to co-star in Sony Pictures' Goosebumps opposite Jack Black, Dylan Minnette and Odeya Rush. Additionally, Sage will also be seen starring in Paramount's Scouts Guide to the Zombie Apocalypse, which centers on a group of Boy Scouts who rise to the occasion as their small town is faced with a zombie outbreak. Sage co-stars alongside Tye Sheridan and Patrick Schwarzenegger.