I'm from England, and I do know a fair few children with nicknames as full names (e.g. my cousin
Alfie, my nieces
Lily and
Abby, my friend
Charlie).
In a way I can understand that, if you plan to use the nickname all the time, there is not much point in using a longer name and having to ask people (teachers, friends etc.) to use the nickname.
Also, I think a lot of these nicknames are cute but the long versions are quite old fashioned and sometimes unattractive. I think a 7-year-old called
Alfred just sounds strange, whereas
Alfie is fine.
On the other hand, I think that a 30-year-old businessman called
Alfie seems a bit strange, and it might be better to have a full name to use in later life and in a professional context.
I don't think it is an age related thing, this trend is really common among parents of all ages as far as I know.