I think some of that is true, some less so.
Young kids getting Dan rank - I don't think they necessarily have the maturity to have earned it fully.
Getting BB in a few years - that's a little more contentious really.
Not really, unless you're confusing maturity within the art with physical/emotional maturity in general. They're not at all the same.
But likewise, if everyone is expected to do 10 years, it gets a bit too much like simply serving time. Is that 10 years of once a month? Twice a year? 3 times a week?
Obviously there is variation by individual, but I don't think I've ever met anyone who had a mature understanding of an art in less than 6-8 years, at a minimum. And most take longer than that.