Old
Use for people to be more polite. It means 'older' or 'elderly'.
Use for things that are very old, like antiques or ancient ruins.
A formal and respectful word for a very old person, like 'elder' or 'senior citizen'.
My phone is old, I need a new one.
My grandfather is an older person.
Is your house new or is it old?
In the museum there are many old/antique objects.
The distinction between using 'viejo' for things and 'mayor' for people is standard across the Spanish-speaking world. Using 'viejo' for a person can be considered rude unless you know them very well.
It is very common and affectionate to refer to your parents as 'mis viejos' (my old folks).
Among friends, 'viejo' can be used as a casual term of address, similar to 'man' or 'dude' (e.g., '¿Qué pasa, viejo?'). Do not use this with strangers.
'Mayor' is the standard polite term for people. 'Anciano/a' is also very common in formal or respectful contexts.
Politeness is key. Using 'persona mayor' is the strongly preferred and respectful way to refer to an older person.
Using 'viejo' to describe a person you don't know well. — This can sound rude, as if you're calling them 'worn out'. Use 'mayor' to be respectful. INCORRECT: 'El señor es viejo.' CORRECT: 'El señor es mayor.'
Forgetting to match the gender of the noun. — Adjectives in Spanish must agree in gender with the noun they describe. 'Viejo' is for masculine nouns and 'vieja' is for feminine nouns. INCORRECT: 'La casa es viejo.' CORRECT: 'La casa es vieja.'
Using 'mayor' to describe an object. — 'Mayor' is used to compare the age of people, not things. For objects, always use 'viejo' or 'antiguo'. INCORRECT: 'Mi carro es mayor.' CORRECT: 'Mi carro es viejo.'