Сто лет не виделись! Вот это да, рад тебя видеть.

No, it is not usually literal here. Сто лет literally means a hundred years, but in everyday Russian it is a very common exaggeration meaning for a very long time, much like English I haven’t seen you in ages.

So:

• Сто лет не виделись! = Long time no see!
• It sounds natural and friendly, not strange or dramatic.

You can also hear similar exaggerations like:

• Сто лет тебя не видел! = I haven’t seen you in ages!

Because виделись means saw each other or met.

The verb видеться / увидеться is the reflexive form used for a mutual action:

• видеть = to see
• видеться = to see each other / to meet

So:

• Я тебя не видел = I didn’t see you
• Мы не виделись = We haven’t seen each other

In this sentence, the speaker is talking about both people, so не виделись is the natural choice.

Because Russian uses the plural for we, even if we means just two people.

The full idea is:

• Мы сто лет не виделись. = We haven’t seen each other in ages.

Russian often drops pronouns when they are obvious from context, so мы is omitted.

That is why the verb is plural:

• виделись = we saw each other / have seen each other

Russian often uses the past tense where English uses the present perfect.

So:

• не виделись literally looks like did not see each other
• but in context it means haven’t seen each other

This is very normal in Russian. Russian does not have a separate tense exactly like the English present perfect, so past-tense forms often cover that meaning.

Because виделись is imperfective, and that fits the idea of a long period during which you haven’t seen each other.

Compare:

• Мы сто лет не виделись. = We haven’t seen each other for ages.
• Мы не увиделись. = We didn’t manage to meet / we didn’t end up seeing each other.

So:

• виделись focuses on the general situation over time
• увиделись would focus more on a completed meeting event

In this expression, the imperfective is the natural choice.

Вот это да is an exclamation showing surprise, amazement, or strong reaction.

Depending on tone, it can mean things like:

• Wow!
• Well, I’ll be!
• No way!
• Would you look at that!

In your sentence, it expresses happy surprise at seeing someone unexpectedly or after a long time.

It is very idiomatic. Literally, the words are something like:

• вот = here / look
• это = this
• да = yes

But you should learn вот это да as a fixed expression, not word-for-word.

Yes. Very often it stands alone as a complete reaction:

• Вот это да!

That is perfectly natural Russian.

In your sentence, it is followed by another comment:

• Вот это да, рад тебя видеть.

So the speaker first reacts with surprise, then adds glad to see you.

Because рад + infinitive is a very common Russian structure.

So:

• рад тебя видеть = glad to see you
• literally: glad [to] see you

This works like English glad to meet you / glad to see you.

You could also say a fuller version like:

• Я рад, что тебя вижу.

But that sounds less natural in this situation. The infinitive structure is the normal idiomatic one here.

Because тебя is the direct object of видеть, and видеть takes the accusative case.

So:

• видеть кого? = to see whom?
• answer: тебя

For the pronoun ты, the accusative form is тебя.

This form is also the same as the genitive form, which is why it may look confusing at first.

Examples:

• Я вижу тебя. = I see you.
• Рад тебя видеть. = Glad to see you.

Because Russian often omits subject pronouns when they are understood from context.

The full sentence would be:

• Я рад тебя видеть.

But in conversation, especially after an emotional exclamation, it is very natural to drop я.

Russian does this much more freely than English.

No. If the speaker is female, it should be рада.

Compare:

• male speaker: рад тебя видеть
• female speaker: рада тебя видеть

This is because рад / рада agrees with the gender of the speaker.

Similarly:

• Я рад вас видеть. = said by a man
• Я рада вас видеть. = said by a woman

Yes, very much so.

Clues:

• Сто лет не виделись! is a friendly, conversational expression.
• тебя uses ты, which is informal singular you.
• The whole sentence sounds warm and spontaneous.

If you wanted a more formal version, you might say:

• Давно не виделись! Очень рад вас видеть.

That would be appropriate when addressing someone with вы.

Yes, absolutely. It is very useful to memorize it as a set phrase.

Native speakers commonly use it as a greeting when meeting someone after a long time.

Useful chunks from this sentence:

• Сто лет не виделись! = Long time no see!
• Вот это да! = Wow!
• Рад тебя видеть. = Glad to see you.

Learning these as ready-made expressions will help you sound much more natural.