Thats certainly true now - albeit whenever it suits youth organisations/funders! I'm fairly sure most young people couldn't care less although I do remember not wanting to be referred to as a "child" at a certain point!
I wrote a blog on a similar subject a few days ago http://www.breakfastsociety.com/2008/07/transition-to-adulthood/
(sorry Cathy think I've overtaken the plugs for your own blog now!) - but I do think as things currently are they're confusing and inconsistent and it would help if there was more a transitional approach between children/youth/young adulthood/adulthood - not just for young people but also for youth organisations.
For a job interview I was once asked to design a programme for 14 - 18 year olds. I started by asking one person to pretend they were 16, another they were 16 and the other they were 18 - and then asked each of them to imagine what they're concerns & interests were at those ages.
My point was that a 14 year old hadn't started their exams at school, the 16 year old may have failed misreably, and the 18 year old may have been in full time work for 2 years already - their stages of life were vastly different, so trying to design a programme for that age range wasn't sensible (I got the job and we agreed instead to focus on 11 - 16 year olds).
Still, I imagine you're right John and for quite sometime it will remain as whenever it suits