“22” was just a joke, because that’s the typical age for a U.S. college graduate.
Film school is highly preferred for several reasons. People who go there are highly dedicated and motivated, they learn all aspects of filmmaking (which makes it easier to write a proper script), and their ability can be more easily judged. And it’s easier to recruit from that pool, just as major corporations go to Business Schools to recruit MBAs.
The alternative is to have a camera in your hand from puberty onward, make lots of short films and then longer films, plunge into the extensive world of film festivals and get a reputation. Or, these days, go online and do computer animation until you get someone’s attention.
Getting attention from somebody is key. Hollywood is a mindset. Nothing exists outside of it. If you are not in Los Angeles and not making contacts you are not going about the business in a professional fashion.
The only exception is to become famous first. Write a Pulitzer-Prize winning novel (Michael Chabon). Become the world’s best-selling author (Stephen King). Believe it or not, it is far easier to get onto The New York Times Bestseller list with your first book than it is to sell a screenplay from outside the business. The former has happened. Somebody may know of a recent example of the latter, but I don’t.
The British film industry is even more insular than Hollywood.
No, they don’t. They lament the lack of $400 million grossing super-spectaculars. Every film studio is already sitting on a pile of literally thousands of scripts that nobody will make.
Critics and other outsiders lament the lack of good scripts, but they don’t count.
You are being wildly over-optimistic. There, does that help?