I have to agree it would depend on the teenager and the situation.  We had a situation come up just recently where all the adults in our family were getting the rare treat of an evening out without the 28 children that we have in our family with my two plus all my nieces and nephews (There are heaps of us)

My brother in laws eldest child (he has 9) is 16 and her and my other niece (13) were to look after the younger children at home.  I chose not to leave my two CAH kids with my nieces due to two reasons: 1 CAH, my nieces know nothing about CAH and how to deal with an emergency situation, 2. It might have been okay if there were not so many other kids to deal with.  I think the girls were actually relieved that there were two less kids to worry about!

If it had been the two older girls and just my two kids I probably would have said yes providing I could clue the girls up on how to deal with CAH.  We also always carry our mobile phones with us.

Good luck with your decision.

Jane