This made me laugh , I disagree with you about most of what you said but thanks for the laugh. I don't see how not allowing people under 20 on the internet would be a massive blow and all that … ( not sure if you're serious and being melodramatic or joking or what ) - you know there's these things called books and parents and other adults could / should teach them basics and stuff about how the internet works without letting them on the internet.
if noone uses the internet until their 20, then they wont be very interested in it as they didn't grow up with it. so you will lose like 95% of potential programmers, game designers, web site developers, etc. people form their hobbys and preferences when their young. keep the internet from them at that stage, and they wont have nearly the interest or knowledge they otherwise would have. for a while you'd be fine. but once all the other generations that were there before the ban are gone or retire, you will suddenly have a lack of web development and there will be a major crisis for all company's that rely on the internet as they cant find enough people qualified/capable for the job. plus all industry's that rely on the internet to market to younger audiences and are made only possible through that will also crash since theres no longer a younger audience. adults wont use the internet as often either since they didn't grow up with the internet so all other industry's will also take a blow as well, just not be destroyed. all in all, you'd wreak anything that relies on the internet (just about everything) by keeping everyone from developing an interest in it when they are in that phase of their life where they develop interests (from when their born to around 20 years old) and therefore minimizing the number of people going into the internet/web/game/digital marketing industry. also, most people already don't use the internet properly or know how to use advanced searching capability's (like image drag and drop is 1 of them), google search advanced filters (not the ones in the tool bar, research data bases, the power of extensions and scripts, proper research, or get reliable news that isn't biased by politics. we dont need to make that any worse than it already is. hell, i bet you dont even know/do half of the simple internet tools/capability's that anyone could easily use that im talking about which is my point. people wont look at those books and will blow off their parents. you forget most people are too lazy or will be to concerned with other things to bother with it.