Poli, 500 years ago, the Siglo de Oro Español was at its peak (Cervantes, Lope de Vega, Calderón de la Barca, Quevedo, etc.). The Spaniards were already speaking it in its most sublime forms and were already exporting it to the Americas and other territories.
Spanish has a much longer history, becoming a language on its own right from the 10th to 13th centuries. It has evolved a lot, pronunciation has changed, spelling has changed and it's being revised by the Academia all the time, adjusting and adopting new letters and sounds (like "w" or "sh"), new spellings, new grammar, etc.