Learn Italian: Mio fratello ha quindici anni e ha sempre fame. - My brother is fifteen years old and he is always hungry.

In English, we say someone is a certain age, but in Italian, people have years. To state an age, you use the verb avere (to have). So, ha quindici anni literally means "he has fifteen years."

Why does it say ha fame for "is hungry"?

Just like with age, Italian uses avere (to have) for physical sensations like hunger, thirst, and feeling cold. Fame is actually a noun meaning "hunger", so ha fame literally translates as "he has hunger."

I learned that possessives usually need words like il or la before them. Why is it just Mio fratello and not Il mio fratello?

You normally do need the definite article, like in il mio cane (my dog). However, there is a special exception for family: when you are talking about a single, close family member like fratello (brother) or madre (mother), you drop the il or la.

Why does sempre (always) go in the middle of ha fame?

In Italian, frequency adverbs like sempre (always) usually go immediately after the verb. Since the verb here is ha, sempre goes right after it, resulting in ha sempre fame.