Funnily enough, teens playing teens is a relatively recent development. The 1950s is usually hailed as the decade which saw the advent of the teen as a rebellious, anti-establishment, anti-parent icon. (In fact, teenagerdom was acknowledged many centuries before that, but the teen as consumer began to come into his and her own in the United States during the prosperous Fifties.) But teen parts were played by people who were, for the most part, at least in their twenties.

In fact, the "teenagers" in Peyton Place (1957) were played by actors in their 30s. Rebel Without a Cause (1955) is sometimes regarded as the ultimate teen film, but its star, James Dean, was 24. There have been many, many teen films, dealing with what are regarded as teen issues (notably "alienation") since then.

As the years have ticked by, films about teenagers have dealt more and more overtly with teenage sexuality, and have consequently got 18 certificates. The ironic result has been adults more and more freaked-out by what they see as the declining moral values of young people; it's ironic because adults have been evaluating the behaviour of teenagers based on films made by adults, starring adults, to which only adults have access.

Increasingly teenage films are starring teenagers, and even though there are references to sex and drugs and alcohol, they are being carefully crafted to get certificates that allow teenagers in.

Of course, this may be less a courageous stance on behalf of teenagers and more a shrewd business tactic. Young people seem to have more and more money to spend (though you might well wonder where these cash-rich young people are!). Certainly, retailers see the teen years as boom consumer time, and more and more products - films, clothes, software, CDs, etc - are teen-oriented.

Did the teenager invent the teenager, or was it some inspired marketing mogul? And what role has mass communication played?