Learn Portuguese (Portugal): O rapaz tem quinze anos.

In English we say someone "is" a certain age, but in Portuguese you say they "have" a certain number of years. The verb ter means to have, so O rapaz tem quinze anos literally translates to "The boy has fifteen years."

Is tem a regular verb?

No, tem comes from the highly irregular verb ter (to have). This is the form you use for he, she, or a formal you. You will use ter often, as it is needed for giving age and expressing physical states like being hungry or thirsty.

Why isn't there a word for "old" in the Portuguese sentence?

In Portuguese, you do not use a word for "old" when giving an age. You simply state the number of years (anos) the person has. Adding a literal translation for old would be incorrect here.

How is the letter z at the end of rapaz pronounced?

In European Portuguese, a z at the very end of a word makes a "sh" sound. So, rapaz sounds like "rah-pash".