Fascinating article on the BBC website saying that psychologists will now be recommended to treat young people http://www.bbc.co.uk/news/magazine-24173194 with the view that adolescence now effectively runs up until the age of 25
I look back at my younger self (not that far back, I'm only a young 33 now 
) and think it sounds about right. I was quite mature for my age and at 18 I left my home country to live in England. I had a sense of responsibility for my own life even then but my god did I not really have a clue. Certainly emotionally speaking I don't think I started to know myself properly until I was 22/23.
I don't know what I think about 'infantilised culture' being the sole reason though. It's a different world we live in to 50 or more years ago so making comparisons is not really helpful. Parents may be a bit more protective towards their children now, which in some context will be detrimental but they are also more emotionally demonstrative, more informed and more involved in their children lives? Anyway it seems to be a bit of a generalisation to me. Not that I have a better explanation for the 30 year old still enjoying living with his parents mind you. Not having a choice economically is one thing, being there because you don't want to take care of yourself is quite another.