Teen Sitcom Definition.

What exactly is the definition of a "teen sitcom"? The reason I ask is that some people on this site seem to narrow it down to things shown on kiddie channels.

Back when I was a lad, or at least around when I was born, the kind of sitcoms teens saw were completely different to what some are using the term for now. Back in the day the BBC for example would be churning out broad appealing sitcoms by the boatload; Dad's Army, Porridge, Open All Hours, Yes Minister, Only Fools & Horses, 'Allo 'Allo, Are You Being Served, Blackadder, Vicar of Dibley and Fawlty Towers to name but a few.

It seems like these BBC classics aren't considered "teen sitcoms" despite the fact that they would have been watched by teens when they were new! I blame Nickelodeon since they started churning out kiddie sitcoms that seem to be all set in an American performing arts school. How does that make it a "Teen Sitcom" exactly?