Justin Bieber is getting his 21st b-day started by partying with a 50-year-old as his buddies have surprised him with a sick ’65 Lincoln Continental. Sources close to the situation tell TMZ that Biebs was rollin’ up and down the Sunset Strip Thursday night in style after his boys John and Sammy Shahidi surprised him at the studio with the completely restored classic. Sources add that the Shahidi’s, JB’s partners in the selfie-app “Shots” — spent around $20K and several months working on the whip which looks just like the one in “Entourage” — one of Bieb’s favorite shows.