Learn Spanish (Latin America): La otra casa es vieja.

While descriptive adjectives (like color, size, or age) usually go after the noun in Spanish, words that tell you 'which one' or 'how many' go before it. Otra (other) points out which house we mean, so it is placed before casa.

Why does the word for 'old' end in an 'a' here (vieja)?

Adjectives in Spanish must match the gender of the noun they describe. Because casa (house) is a feminine word, the basic dictionary form viejo changes its ending to vieja to match it.

Does otra also change its ending to match the noun?

Yes! Just like vieja, otra must match the gender and number of the noun it belongs to. If you were talking about a masculine noun like a car (carro), you would say el otro carro.

Why do we use es instead of está for 'is'?

We use es (from the verb ser) because being old is considered a defining, permanent characteristic of the house. The other verb for 'to be' (estar) is used for temporary states, conditions, or locations.