At what age should foreign language learning begin?

Like Shakespeare’s enumeration of the ages of man the possible answers to this question are seven-fold:

1 Never 2 In adulthood, at the point of need/desire/interest 3 During adolescence as an option or under compulsion 4 At the beginning of the secondary cycle 5 During the later primary years 6 Throughout the years of primary schooling 7 As early as possible

We consider the implications of each of these in turn.