Скільки тобі років?

Word by word:

• Скільки = how many / how much
• тобі = to you
  This is the dative form of ти
• років = years
  This is the genitive plural form of рік = year

So the sentence is literally something like How many years to you?, but it means How old are you?

Because Ukrainian expresses age with the dative case, not with a subject like English does.

English says:

• You are 20 years old

Ukrainian says:

• Тобі 20 років
• literally: To you, 20 years

So ти changes to тобі because the sentence uses the idea to you.

A few related forms:

• мені = to me
• тобі = to you
• йому = to him
• їй = to her
• нам = to us
• вам = to you

In Ukrainian, the present-tense verb to be is often omitted.

So where English says:

• How old are you?

Ukrainian simply says:

• Скільки тобі років?

There is no spoken are/is here, and that is completely normal.

Because after скільки and after numbers like 5 and higher, Ukrainian normally uses the genitive plural.

That is why you get років.

Compare:

• 1 рік
• 2 роки
• 3 роки
• 4 роки
• 5 років
• 10 років
• скільки років

So in Скільки тобі років?, років is the expected form.

The structure is basically:

• Скільки = how many
• тобі = to you
• років = years

So the literal pattern is:

• How many years to you?

That may sound strange in English, but it is the normal Ukrainian way to ask age.

A standard answer is:

• Мені 20 років. = I am 20 years old.

More examples:

• Мені 1 рік.
• Мені 2 роки.
• Мені 18 років.
• Мені 32 роки.
• Мені 45 років.

Notice the noun changes:

• 1 рік
• 2, 3, 4 роки
• 5+ років

In casual speech, people may shorten it, but Мені ... років / роки / рік is the safest standard pattern for learners.

Yes. тобі is the informal singular form, used with:

• friends
• children
• family
• people you know well

For polite speech or for more than one person, use:

• Скільки вам років?

That can mean either:

• How old are you? politely, to one person
• How old are you? to several people

Yes, Ukrainian word order is fairly flexible.

The most neutral and standard version is:

• Скільки тобі років?

You may also hear:

• Тобі скільки років?

That can sound more conversational or place extra focus on тобі.

As a learner, it is best to use Скільки тобі років? first.

A rough English-friendly guide is:

• SKEEL-ky to-BEE ro-KEEV

Approximate stress:

• Скільки → stress on the first syllable
• тобі → stress on the last syllable
• років → stress on the last syllable

This is only approximate, but it is a good starting point.

Usually Скільки asks about quantity, so it often means how many or how much.

In this sentence, it is naturally understood as how many, because років means years, which are countable.

So:

• Скільки тобі років?
  literally = How many years to you?

Yes. This is the standard everyday way to ask someone how old they are.

Even though English uses old, Ukrainian normally uses years:

• English: How old are you?
• Ukrainian: Скільки тобі років?

So this is not a strange or unusual phrase. It is the ordinary, natural way to ask.