If you are not born in Spain and you do not have any parent with Spanish nationality you may be interested in other ways of getting the nationality.
Foreigners can opt for Spanish nationality if they have been subject of a parental authority of a Spaniard, if one of their parents was born in Spain, if they have been adopted by Spaniards after the age of eighteen and if the birth in Spain or parentage is determined (establishing one person’s parents).
Those who are able to apply for the Spanish nationality are: the legal representatives if the solicitant is a minor, people over the age of fourteen and those individuals who are already emancipated. To carry out all the formalities you need to go the Civil Registry of the place of residence.
Another way to get the Spanish nationality is via Residence and it is only for people who have been legal residents of Spain during an uninterrupted period of ten years before the day of application. In this case, people who can opt for the nationality are people over eighteen or emancipated, those who are over 14 and are assisted by their legal representatives, legal representatives of minors under 14 and legal representatives of people who have been declared incapacitated.
Source: Spanish Ministry of Foreign Affairs and Cooperation