Why is galician considered a language?

Galician is actually older than castillian (spanish) and most linguists consider it to be more close to portuguese than to any other idiom, actually, before Portugal was created, in the 12th century, there was a gallician-portuguese language, galaico-portugu�s, suggesting there was a linguistic and cultural union between the kingdom of Galicia and the County of Portus Cale (the ancestor of Portugal).