Mi hermana cumplirá veintiún años en mayo, y ya tiene pensado invitar a toda la familia.

My sister will turn twenty-one in May, and she is already planning to invite the whole family.

Breakdown of Mi hermana cumplirá veintiún años en mayo, y ya tiene pensado invitar a toda la familia.

• la familia: the family
• en: in
• mi: my
• a: to

Questions & Answers about Mi hermana cumplirá veintiún años en mayo, y ya tiene pensado invitar a toda la familia.

Why is cumplirá used here?

Cumplirá is the simple future of cumplir. In this sentence, cumplir veintiún años means to turn twenty-one.

So:

• Mi hermana cumplirá veintiún años en mayo = My sister will turn twenty-one in May

In Spanish, cumplir + number + años is the normal way to talk about reaching a certain age.

You could also hear va a cumplir veintiún años, which is the going to future. Both are correct, but cumplirá sounds a bit more neutral and straightforward in written Spanish.

What does cumplir años mean exactly?

Literally, cumplir means something like to complete or to fulfill, but with age it means to turn a certain age.

Common patterns:

• cumplir años = to have a birthday / to turn a year older
• cumplir veinte años = to turn twenty
• ¿Cuándo cumples años? = When is your birthday?

So in this sentence, cumplirá veintiún años does not mean she is completing twenty-one years in some abstract sense; it is simply the normal Spanish way to say she will turn twenty-one.

Why is it veintiún años and not veintiuno años?