Stengel was born in
Lørenskog, and grew up in
Hokksund, where he played for
Hokksund before he joined
Stabæk as a youth. He started playing for their senior B team,
Stabæk 2, and became the youngest goalscorer ever in the
Norwegian Second Division. In May 2010 he scored his first senior goal at the age 14 years and 261 days. In 2009, Stengel did a trial at
Manchester United together with
Mats Møller Dæhli, who later joined the club's academy and
Sondre Tronstad. In December 2012, Stabæk granted Stengel a week to trial with
PSV Eindhoven. On 2 October 2011, Stengel made his
Norwegian Premier League debut, starting the match against
Sarpsborg 08. Aged 16 years and 37 days, he became the youngest Stabæk-player to start a match in Tippeligaen, and the then third youngest player in the Norwegian top division. Stengel became known during the autumn of 2011, as he was a piece of
Veigar Páll Gunnarsson's transfer to
Vålerenga, which caused great
controversy.
TV 2 (Norway) revealed on 12 October 2011 that Gunnarsson was transferred to Vålerenga for 1 million NOK, while Vålerenga paid a transfer fee of 4 million NOK for an option for the then 15-year-old footballer Stengel. In February 2012, Stengel stated that he wants to be known as a footballer, not as the guy who was a piece in the controversial football transfer, and that his dream is to play in one of the best leagues in Europe. After Stabæk was relegated from Tippeligaen in
2012, Stengel was one of the key-players in the young Stabæk-team that finished the
2013 season second in the
First Division and won promotion back to Tippeligaen. His contract with Stabæk expired after the season and he joined Vålerenga as a free agent ahead of the 2014 season, signing a four-year contract with the club. On 20 November 2017,
Strømsgodset Toppfotball announced that Stengel had signed a three-year deal from 1 January 2018. ==International career==