Çocuk on yaşında.

In Turkish, the present-tense form of to be is often not stated as a separate word in the 3rd person. So Çocuk on yaşında naturally means The child is ten years old, even though there is no standalone word for is.

This is very normal in Turkish:

• Ben mutluyum = I am happy
• O mutlu = He/She is happy

So here, on yaşında works as the predicate, and the 3rd-person copula is understood.

Yaşında is the standard word used in Turkish for expressing someone’s age in the pattern number + yaşında.

You can think of on yaşında as meaning at the age of ten or simply ten years old.

If you want the grammar behind it, yaşında comes from:

• yaş = age
• -ı = a 3rd-person possessive element
• -nda = locative ending, with a linking n

But for learners, the most useful thing is to treat X yaşında as a fixed pattern:

• beş yaşında = five years old
• on yaşında = ten years old
• yirmi yaşında = twenty years old

After numbers, Turkish usually keeps the noun in the singular. This is a general rule, not just for age.

For example:

• iki kitap = two books
• üç gün = three days

So with age, Turkish says on yaşında, not a plural form of yaş. English uses years, but Turkish does not need that plural marking after a number.

This is the normal Turkish order for a simple sentence: subject + predicate.

Here:

• Çocuk = subject
• on yaşında = predicate

Turkish very often places the main predicate at the end of the sentence, so Çocuk on yaşında sounds neutral and natural.

Çocuk on yaşında is a full sentence: The child is ten years old.

On yaşında bir çocuk is a noun phrase: a ten-year-old child.

So the difference is:

• Çocuk on yaşında = statement
• on yaşında bir çocuk = description of a noun

This is a very useful contrast in Turkish.

Turkish does not have articles like English the and a/an in the same way. So çocuk can mean the child, a child, or just child, depending on context.

If you want to make it clearly indefinite, Turkish often uses bir:

• Bir çocuk on yaşında = A child is ten years old

In an isolated example like Çocuk on yaşında, English often translates it as The child is ten years old, but the exact choice depends on context.

With I and you, Turkish usually adds personal endings:

• Ben on yaşındayım = I am ten years old
• Sen on yaşındasın = You are ten years old
• O on yaşında = He/She is ten years old

So the basic age expression stays the same, but the sentence gets a personal ending unless it is 3rd person.

Yes. Çocuk on yaşındadır is grammatically correct.

The ending -dır can add a more formal, definite, explanatory, or written tone. In everyday speech, people usually just say Çocuk on yaşında.

So:

• Çocuk on yaşında = normal, everyday
• Çocuk on yaşındadır = more formal or emphatic

To talk about age in Turkish, the normal pattern is number + yaşında.

• yıl means year in a calendar/time sense
• yaşlı means old / elderly

So:

• on yaşında = ten years old
• on yıl does not work for age in this way
• on yaşlı is not how Turkish says ten years old

This is one of those expressions you should learn as a set phrase.

A rough guide is:

Çocuk ≈ cho-jook

• ç sounds like ch in chair
• c sounds like j in jam

on ≈ on with a short o

yaşında ≈ ya-shın-da

• ş sounds like sh
• ı is a Turkish vowel with no exact English equivalent; it is not the same as i

So a rough full pronunciation is:

cho-jook on ya-shın-da

If you want to sound more natural, pay special attention to ı, because that is often the trickiest sound for English speakers.