That's not entirely true. Youtube is based on what Society Favors as "Talented". Since Society tends to favor to "Young, Beautiful, Sexy, Hot, Amazingly Stupid, or Never seen before content".
You can be beautiful and young all you want. That's no guarantee of success. And you can be not so good looking and not so young and still be successful. It's a fact, it's not a theory.
Society actually gives an opportunity to all types of people. The big dogs are the ones who don't give opportunities. The big companies, the studios, that think people will only accept someone beautiful. There's no factual evidence of that.
The reason why anyone can be successful on Youtube is because there's no big CEO deciding who can have air time and who can't. The audience is the boss, the audience decides, and the result of that is that you can find all types of people having success on youtube: Fat, slim, tall, short, white, black, young, old. This is just a fact dude. You can find plenty of examples of all these types of people being successful. It's a fact.
Now, you might say "oh, but most of them are young and bla bla bla". Well, most people who decide to participate on youtube are young, so yeah, you're gonna get more young people in the spotlight, which doesn't mean there isn't room for anyone else.