The condition is that it requires non-stop flights.
For those coming from or going to "feeder cities", there are often no direct flights. That's what the issue is for our friends as they are both coming from, and, going to feeder cities in the U.S.
For us, no U.S. airline offers direct flights from the U.S. West coast to Geneva. There are many routes but they are all connections through NY, Chicago, Atlanta, Dallas, etc. Swiss Air also has no direct flights from the U.S. West to Geneva, but they do have direct flights from an airport over three hours drive from our home to Zurich. Six hours driving round-trip is a hassle but at least possible (sometimes requiring an airport hotel stay for very early or late flights). From Zurich it's an easy one hour flight to Geneva and from there a couple hour train ride to the school. Fortunately, Swiss Air (and a lot of international airlines) have no problem with 13+ year-olds connecting. It's been 13+ for a long time because I did it internationally when I was a kid - and that was the era of carbon triplicate paper tickets and no cell phones :-).
I think Lufthansa changed their policy a few years ago only because they code share so much with United. It's really the U.S. airlines that started changing from 13 to 16 being the minimum for unaccompanied connections. I suspect a U.S. airline had some unaccompanied connecting teen go AWOL and got sued over it, then their lawyers decided the legal exposure just wasn't worth it. Unintended consequence: free-range and outward bound Summer camp and school experiences got a lot more expensive and challenging for U.S. 13 to 15 year-olds. The international boarding school our daughter attends is terrific (and going was her idea). It has students from over 80 countries but they told us there are a lot fewer from the U.S. in the last five years.
For those coming from or going to "feeder cities", there are often no direct flights. That's what the issue is for our friends as they are both coming from, and, going to feeder cities in the U.S.
For us, no U.S. airline offers direct flights from the U.S. West coast to Geneva. There are many routes but they are all connections through NY, Chicago, Atlanta, Dallas, etc. Swiss Air also has no direct flights from the U.S. West to Geneva, but they do have direct flights from an airport over three hours drive from our home to Zurich. Six hours driving round-trip is a hassle but at least possible (sometimes requiring an airport hotel stay for very early or late flights). From Zurich it's an easy one hour flight to Geneva and from there a couple hour train ride to the school. Fortunately, Swiss Air (and a lot of international airlines) have no problem with 13+ year-olds connecting. It's been 13+ for a long time because I did it internationally when I was a kid - and that was the era of carbon triplicate paper tickets and no cell phones :-).
I think Lufthansa changed their policy a few years ago only because they code share so much with United. It's really the U.S. airlines that started changing from 13 to 16 being the minimum for unaccompanied connections. I suspect a U.S. airline had some unaccompanied connecting teen go AWOL and got sued over it, then their lawyers decided the legal exposure just wasn't worth it. Unintended consequence: free-range and outward bound Summer camp and school experiences got a lot more expensive and challenging for U.S. 13 to 15 year-olds. The international boarding school our daughter attends is terrific (and going was her idea). It has students from over 80 countries but they told us there are a lot fewer from the U.S. in the last five years.