Scooter Braun has retired as a music manager. The 42-year-old entrepreneur – who has worked with the likes of Justin Bieber, Ariana Grande and Demi Lovato during his career – has taken to social media to announce that he’s retiring from music management after 23 years. He wrote on Instagram: “I have been blessed to have had a ‘Forrest Gump’-like life while witnessing and taking part in the journeys of some of the most extraordinarily talented people the world has ever seen. I’m constantly pinching myself and asking ‘how did I get here?’ And after 23 years this chapter as a music manager has co…