A blend of the nouns screen and teenager, the portmanteau screenager denotes a teenager who is fully conversant with, and skilled in, the use of computers and other electronic devices.
However, I have discovered that screenager was occasionally used before the computer era.
In the following from The Ottawa Citizen (Ottawa, Ontario, Canada) of Saturday 21st September 1957, screen-agers and scream-agers—perhaps both coined for the occasion—denote teenagers reacting to the appearance of the English singer Tommy Steele (Thomas Hicks – born 1936) at the screening of his film:
LAW AND DISORDER
Call them teen-agers, “screen-agers”, or “scream-agers”, the Rock and Roll fans are the same enthusiastic youngsters in any country. Here, at the Anglais Theater, in Stockholm, Swedish fans of singer Tommy Steele need police restraint to curb their excitement over the singer’s personal appearance with the showing of his film, “The Tommy Steele Story”. One “shook up” miss (at right) appears barefooted after apparently losing her shoes in the melee.—UP Photo
And the second-earliest instance of screenagers that I have found denotes teenagers as they are represented in motion pictures and television series—it is from The Hartford Courant (Hartford, Connecticut) of Sunday 1st September 1985:
Motion picture cameras are out of focus when zeroed in on teenagers, says 19-year-old Justine Bateman* of TV’s “Family Ties” series. They are misrepresented as sex-crazed, mindless hedonists in such movies as “Porky’s,” “Weird Science,” “Real Genius,” she says, giving TV slightly better marks for being “accidently” more realistic in treatment of teens, thanks to network censorship prohibiting nudity, drug-taking and drunkenness. “All the emphasis on sex in teenage pictures is ridiculous. In real life it mostly involves girls who get drunk at parties and then are taken advantage of. Teenagers are more serious about school than they are shown in movies and TV. Movies keep showing kids at parties trashing somebody’s home. And then you never see the parents reacting to it. That doesn’t happen. Who is going to let a guy ride a motorcycle in their house?” Why, then, are teen movies cleaning up at the box office? “Because that’s all there is out there,” Bateman says. “If there’s nothing that interests young people on TV, they go out to movies.” Some aspects of teen-oriented movies are more or less faithful to reality, she says. “The wardrobe in movies for teens doesn’t set trends. Mostly the movies copy what kids wear today. Usually they underplay what teenagers wear. Kids take more chances with their wardrobes. Sometimes the dialogue reflects the way teenagers really talk, but most of the time it’s cliché. Unless the writers have teenagers around the house, they can’t keep the expressions and slang up to date. The best thing movies reflect about teenage tastes is music. And it’s easy. All they have to do is use top 40 stuff.” She also resents the propensity of producers to lump all teenagers into categories — valley girls, jocks, nerds, cheerleaders, as in “The Breakfast Club.” “It was an honest try, but it was also a symbolic representation of high school character clichés,” she says. “Then they make pictures like ‘Weird Science.’ I knew kids that were into science in school, but they weren’t anything like the characters in that movie.”
* Justine Tanya Bateman (born 1966), American author, director, producer and actress
The earliest instance that I have found of screenager in its current sense is from Homes are prime PC frontier, by Tom Foremski, published in the San Francisco Examiner (San Francisco, California) of Sunday 19th June 1994:
New magazines are rapidly being launched to target the home market. Oakland-based Blast Publishing Inc. is preparing to launch a major national magazine called Blast, which, according to Publisher Doug Millison, will be a “lifestyle magazine aimed at ‘screenagers’ — teenagers and twentysomethings that have grown up with PCs and video games.”