Learn Portuguese (Portugal): O aluno tem dezoito anos. - The student is eighteen years old.

In Portuguese, age is expressed using the verb ter (to have). Instead of saying someone is a certain number of years old, you say they have those years. Since o aluno (the student) is third-person singular, we use tem, which means "has".

Where does the word dezoito come from?

Dezoito is the number eighteen. It is literally a combination of dez (ten) + e (and) + oito (eight). Over time, these parts merged into the single word dezoito.

If the student were female, would the rest of the sentence change?

The noun and its "the" word (definite article) would change to match the feminine gender, becoming A aluna. However, the verb tem stays exactly the same, giving us A aluna tem dezoito anos. The verb form tem is used for both "he" and "she".

Can I just say O aluno tem dezoito and leave out the word anos?

You can in casual conversation if the topic is already clearly about age, just like saying "He is eighteen" in English. However, the standard and most natural way to state someone's age as a standalone sentence in Portuguese is to include anos (years).