[dagw]

"you're not mature enough to do this"

Isn't it rather saying that you're not experienced enough to do this. Speaking only for myself, I passed my driving test no problem and after a couple of month of driving I thought I was a great driver. Yet looking back now with the benefit of experience I know for a fact I did some really stupid things that first year of driving and it was only luck rather skill that led to me not getting into an accident.

[gambiting]

Again, that would make sense if it applied equally for all new drivers - but if you're over 25 then there is no such restriction, even if you got your licence a day before. You have zero experience behind the wheel but you're fine to drive in a car full of people, but someone who has been driving for 7 years but is one day short of 25 can't do it - who is the more experienced driver there?

So yeah, it's all about "not being mature enough".