Kingship
The matter of who would lead a Celtic group seems to have been decided by a prominent group of nobles rather than by divine right or primogeniture (i.e., the throne being passed to the eldest son or daughter as the case may be).
Although these data are circumstantial (recall that the Celts left no written record), it appears that Kings were chosen on the basis of who was the fittest mentally and physically for the job rather than by kinship to the current King. The King was expected to be strong in order to insure the survival of the group. As you would expect, the King’s successor was chosen prior to his death to insure a peaceful transition of power. There is clear evidence that some rulers were women, but the case for a matrilineal Kingship is weak. It is likely that in the absence of a suitable man in a fundamentally patrilineal system that a strong woman emerged as the most suitable ruler. These rulers were of noble birth in that the ruler was selected from among the ruling elite not from any other strata of society.