What age should you leave a teenager home alone overnight?

[purpleroses]

DP and his ex are in dispute about whether his DD1 is old enough to be left alone at home overnight. To get some perspective, what age did you first/would you leave your teenager on their own a) overnight b) for a weekend and c) for a full week?

(teenager is normally sensible and reasonably mature but sociable and inclined to push boundaries.)

DS is nearly 15 and very sensible. 16 for a night. Not a whole weekend until 17/18. Would you not think about her bringing along a friend on holiday?

We might think about her bringing a friend except we have 6 DCs between us so that would be rather a lot.