I find it highly childish to go out every weekend, get splattered on a pavement somewhere and call it "of age", its just utterly boring and repetitive.
Beyond this, with rising life expectancy statistically hitting 100+ for people born in the last 20 years... it is probably just sensible to also raise the period of childhood...frankly I have always believed you dont really enter adulthood until your late 20s anyway, I don't think 18 years is particularly enough to experience life in a reasonable manner without being gifted a good start in the first place.
As a logical person that enjoys a bit of numbering, if you can live to 100, i would think you were a child for at least 25% of that, 50% being an adult and retiring into the last 25% (i've seen some slick 75 year old's)...
Seems good to me.