Моїй тітці вчора виповнилося сорок років.

Because Ukrainian often expresses age with a construction that literally means something like to my aunt, forty years became complete / were reached.

So in Моїй тітці вчора виповнилося сорок років, the person having the birthday is not treated as the grammatical subject in the way English does with My aunt turned forty. Instead, Ukrainian uses the dative for the person concerned:

• моїй тітці = to my aunt

This is very common in Ukrainian with age:

• Мені двадцять років. = I am twenty years old.
• Йому виповнилося тридцять. = He turned thirty.
• Нашій доньці скоро виповниться п’ять років. = Our daughter will soon turn five.

So моїй тітці is dative because the structure is built around it became forty years to my aunt, not around my aunt as the subject.

This is one of the most important things to notice in the sentence.

Виповнилося is past tense, neuter singular, and it agrees with an understood neuter idea such as it or with the age expression as a whole. In this kind of impersonal construction, Ukrainian does not make the verb agree with тітка.

So:

• моїй тітці = dative, not the subject
• виповнилося = neuter singular past
• сорок років = the age that was reached

You can think of it as similar to an impersonal English pattern:

• It turned out that…
• It happened that…

Here the Ukrainian idea is roughly:

• To my aunt, it became forty years yesterday

That is why you get виповнилося, not виповнилася.

Here виповнилося means turned, reached the age of, or more literally became complete.

It comes from the verb виповнитися / виповнюватися, which in this context is used for age:

• Мені виповнилося 18 років. = I turned 18.
• Йому виповнилося 50. = He turned 50.

So in this sentence:

• Моїй тітці вчора виповнилося сорок років.
• My aunt turned forty yesterday.

This verb is specifically common in age-related statements and birthdays.

The ending -ся is the reflexive/post-verbal particle often seen in Ukrainian verbs. In many cases, it does not translate directly into English word-for-word, but it is part of the verb’s normal form.

Here, виповнилося is the standard form used in this age expression. You should really learn the whole pattern together:

• комусь виповнилося + number
• someone turned + number

Examples:

• Мені виповнилося двадцять. = I turned twenty.
• Братові виповнилося десять років. = My brother turned ten.

So although -ся historically has reflexive origins, in this sentence it is simply part of the verb form you need for this construction.

Because numerals affect the form of the noun that follows them.

After 5 and higher, Ukrainian normally uses the genitive plural:

• 5 років
• 10 років
• сорок років

So:

• рік = singular nominative
• роки = nominative plural
• років = genitive plural

Since сорок is higher than 4, the correct form is років.

Compare:

• 1 рік
• 2 роки
• 3 роки
• 4 роки
• 5 років
• 21 рік
• 22 роки
• 25 років

So сорок років is exactly what you would expect.

Yes, often it can.

In everyday speech, Ukrainian speakers very often omit років when the meaning is obvious:

• Моїй тітці вчора виповнилося сорок.

This still means My aunt turned forty yesterday.

Including років sounds a bit fuller and sometimes slightly more formal or explicit, but both are normal.

Because that mixes English-style thinking with a Ukrainian structure that works differently.

The incorrect version has two problems:

1. Моя тітка is nominative, but this construction wants the person in the dative:

   • correct: моїй тітці

2. виповнилася is feminine, agreeing with тітка, but this construction normally uses the neuter singular impersonal form:

   • correct: виповнилося

So the correct pattern is:

• [dative person] + виповнилося + age

Examples:

• Мені виповнилося двадцять.
• Сестрі виповнилося п’ятнадцять років.
• Моїй тітці вчора виповнилося сорок років.

The word order can change. Ukrainian word order is fairly flexible, and moving вчора changes emphasis more than basic meaning.

All of these are possible:

• Моїй тітці вчора виповнилося сорок років.
• Вчора моїй тітці виповнилося сорок років.
• Моїй тітці виповнилося сорок років вчора.

The most natural choice depends on what you want to emphasize:

• Вчора first: emphasizes yesterday
• Моїй тітці first: emphasizes my aunt
• сорок років later in the sentence: keeps the age as the new information

So the given sentence is natural, but not the only possible order.

It is past tense of a perfective verb.

That makes sense because turning forty is a completed event happening at a specific moment:

• yesterday she turned forty

Perfective verbs in Ukrainian are often used for completed, one-time events. So:

• виповнилося = was reached / turned as a completed fact

If you wanted a future completed event, you could say:

• Моїй тітці завтра виповниться сорок років.
• My aunt will turn forty tomorrow.

Great question. These two sentences are related, but they are not the same.

• Моїй тітці сорок років. = My aunt is forty years old.
• Моїй тітці вчора виповнилося сорок років. = My aunt turned forty yesterday.

So:

• Моїй тітці сорок років describes her current age.
• виповнилося сорок років focuses on the moment she reached that age.

This is similar to the difference in English between:

• She is forty
• She turned forty yesterday

The most useful stress patterns here are:

• моЇй
• тІтці
• вчорА
• виповни́лося
• сОрок
• рокІв

A learner especially needs to watch моїй and років, because the stress may not fall where an English speaker expects.

If you say the whole sentence naturally, it sounds roughly like:

• моЇй тІтці вчорА виповни́лося сОрок рокІв

Yes, absolutely. This is a very normal Ukrainian way to say that someone turned a certain age.

Common patterns include:

• Мені виповнилося двадцять. = I turned twenty.
• Сину виповнилося три роки. = My son turned three.
• Бабусі виповнилося сімдесят років. = Grandmother turned seventy.

So the sentence Моїй тітці вчора виповнилося сорок років is fully natural and idiomatic. It is exactly the kind of structure learners should get used to, because it differs from English in a very typical Ukrainian way.