Scratch 18, I'd say 13. As soon as they become teenagers is when they need to take accountability for their actions. Not doing so is when these 18-year-olds, with some new found freedom, run rampant, believing daddy will bail them out of trouble.
I agree that around that age is when they're old enough to see if they're parents aren't the best role models.
Even if the parents are the ones at fault, the child is the one who must take responsibility for their actions in order to realize their mistakes and change.
For raising children my philosophy is;
Kids grow into Adults.
Trying to make the impossible, possible !