It's common in the UK to work from the age of 13 or 14, depending where you live. I worked in the Post Office across my road at 13, every Wednesday evening and Sunday afternoon, in 2009. Most of my friends had part time jobs working in retail while at school. I was behind the pub bar at 16 slinging pints.
The (possibly completely incorrect) impression I get from speaking with Americans I know who have moved here, or I work with, is that nobody really works until they get to college unless it's a paper round or it's at your parents business. It almost goes without saying then that most people would be pretty infantile if they don't start work until they're almost mid-20s.
I am in Sydney, Australia.
It was a nice surprise to see teenagers working in my local brewery this past weekend, collecting glasses, clearing and cleaning tables, etc. They were probably between 13 and 16. Not allowed to serve alcohol until they are 18, and can take on the personal legal responsibilities for Responsible Service of Alcohol.
Most jobs for teenagers here are in fast food service - two of my friends have mid/late teenagers working these jobs. Most jobs in retail, at least near me, seem to be taken by adults.
Yeah, I think I started working in Restaurants aged 14 and really didn't stop. I still get a slight burst of nostalgia whenever I go to the countryside and see the pubs etc staffed by young'uns(it doesn't seem to happen much in London, don't know about other cities).
I think part of that in Britain is because we live in towns. In a small town there's always a shop or pub or restaurant to work in and kids can walk or cycle to work. Same in NL. Because so much of America lives in pure residential suburbs, the opportunities aren't there.