Hij is zeventien jaar.

The full, explicit version is Hij is zeventien jaar oud.

In everyday Dutch, oud is often left out when it is already obvious that you are talking about someone’s age. So Hij is zeventien jaar is understandable and natural in context.

You can also shorten it even more to Hij is zeventien.

After an exact number, Dutch usually uses jaar:

• drie jaar
• tien jaar
• zeventien jaar

Jaren is more common in less exact or more general expressions, such as vele jaren or jaren later.

So in age expressions with a specific number, jaar is the normal form.

Yes. That is very common.

When the context is clearly about age, Dutch often drops jaar and oud. So all of these can work:

• Hij is zeventien.
• Hij is zeventien jaar.
• Hij is zeventien jaar oud.

The last one is the fullest version.

• Hij = the subject pronoun, meaning he
• is = the third-person singular form of zijn (to be)
• zeventien = the number seventeen
• jaar = year, used here in an age expression

So the pattern is:

subject + form of zijn + number + jaar (oud)

Because in a normal Dutch main clause, the finite verb usually comes in the second position.

Here that gives:

• Hij = first element
• is = finite verb in second position
• zeventien jaar = the rest

That is standard Dutch word order.

Dutch does not use an article in this kind of age expression.

So you say:

• Hij is zeventien jaar.
• Hij is zeventien jaar oud.

Not een jaar here.

The number itself already gives the quantity, so no article is needed.

For a yes/no question, Dutch usually puts the finite verb first:

Is hij zeventien jaar?

You can also use the fuller version:

Is hij zeventien jaar oud?

You usually add niet:

• Hij is niet zeventien jaar oud.
• Hij is niet zeventien.

If you mean not yet seventeen, Dutch often says:

• Hij is nog geen zeventien.

That is a very common phrasing.

A rough English-style guide is ZAY-vuhn-TEEN.

The main stress is on the last syllable: -tien.

Also, hij is pronounced roughly like high.

These are only approximations, but they are helpful for getting started.

Both are possible.

• Hij is zeventien jaar.
• Hij is 17 jaar.

In everyday writing, digits are very common. In textbooks, exercises, and more careful writing, the number is often written out as a word.

Yes. In Dutch, numbers like dertien, veertien, vijftien, zestien, zeventien, achttien, and negentien are written as single words.

So zeventien is correct, not two separate words.