Learn Spanish (Spain): Mi abuelo tiene setenta y dos años. - My grandfather is seventy-two years old.

In Spanish, numbers from 31 to 99 are always written as three separate words connected by y (and). So, 72 is literally seventy and two (setenta y dos). This is different from the twenties, which are joined into a single word like veintidós.

Why does the sentence use tiene instead of the Spanish word for is?

In Spanish, you don't be an age; you have years. Tiene means he has (from the verb tener, to have). So the sentence literally translates to: My grandfather has seventy and two years.

I always mix up 60 and 70. How can I remember that setenta is 70?

It is a very common mix-up! Look at the spelling: sesenta (60) has an s in the middle, just like seis (6). Setenta (70) has a t in the middle, just like siete (7).

Is the wavy line over the n in años really necessary?

Yes, it is extremely important! The letter ñ is a completely separate letter from n in the Spanish alphabet. If you leave off that wavy line (called a tilde), the word becomes anos, which means anuses instead of years.