Matt Wolf's engrossing documentary Teenage looks at the comparatively new phenomenon known as "being a teenager," a concept that the film argues didn't really exist until the mid-1940s. The emotional fulcrum is four real-life historical teenagers: Brenda Dean Paul, a 1920s London flapper; Melita Maschmann and Tommie Scheel, a Hitler Youth and anti-Nazi Swing kid, respectively; and Warren Wall, a 1940s Boy Scout who found he was unable to become an Eagle Scout due to being black. Teenage takes the Ken Burns approach, with actors providing voiceover narration for the historical figures, but goes a step further: Since no actual film footage exists of these four teenagers, there's a great deal of newly staged footage mixed in with the archival films. The new (it's tempting to use the word "fake") material is expertly done, but it's also a little disconcerting. It's not that this sort of mixture can't be done effectively — last year's mountain-climbing doc The Summit pretty well nailed it — but there's a risk of degrading the power of the real footage if a distinction isn't made, particularly when representing issues such as the rise of German fascism concurrent with institutional American racism. None of which takes away from Teenage's sheer entertainment value — as long as those kids stay off my damn lawn.