I ha've known him for approximatelybout 14 years.

Yours is also correct, but I think this sounds more natural for the topic.

WhichThat means we grew up and went to school together.

I'm not sure about this. What I remember from grade school tells me 'which' can't be the subject of independent clauses. I suggested what sounds best to me.

We werehave been in the same class since the beginning of school.

Assuming you're still in the same class now, then it should be 'have been'. 'Were in the same class' suggests that now you aren't in the same class anymore.

edit: I got to the end and just realized you aren't in the same class anymore, so I just recommend saying something like this:

'We were in the same class since the beginning of school until ____.'

or

'We were in the same class throughout school.'

However, we started to communicatehang out when we were oin athe 5 th grade at school.

Communicate is correct, but again, 'hang out' or 'spend time together' are both more appropriate given the subject.

At thatis moment we are close to each other.

Firstly, he is so ambitious that sometimes I wasam surprised.

He is planning to be successful in the future and takinge part in one of the biggest engineering companies in Russia.

Илья классный )

Secondly, I believe that he is very reliable.

He helps me willinglythout hesitation and he gives worthygood advice to me.

Your version is also good. 'worthy' advice sounds a bit too literary for the subject.

On the other hand he could be described as being perhaps as a bit of judgemental.

Small mistakes.

However, I get on with him, and he also accepts my disadvantages.

Lastly, I appreciate that we could bean stay in touch with himeach other despite our distance.

We dohave not grown apart from each other.

'We do not grow apart from each other' implies to me that the two of you are actually, literally incapable of growing apart, which I don't think is what you meant.

Our calls via Skype isare full of jokes, fun stories and also sensitivemore serious topics.

Finally, I could say that I’m happy having a friendship with ilia.

instead of 'having a friendship' I would write 'being friends'

W, which means we grew up and went to school together.

This sentence is a sentence fragment. You should connect it to the sentence before it so that your idea reads "I have known him for approximately 14 years, which means we grew up and went to school together." :)

However, we started to communicate when we were oin athe 5 th grade at school.

In English, the grammatically correct preposition (a preposition is a word like "in," "on," "at," "to," "for," etc.) for this phrase is "in," not "on."

AtSince thatis moment, we are close to each otherhave been close.

You could also say "We have been close to each other ever since then." It doesn't make sense in English to say "At that moment, we are close to each other," even though most people will understand what you're trying to say in this context. :)

He is planning to be successful in the future and takinge part in one of the biggest engineering companies in Russia.

I assume that your friend Ilia is not currently taking part in this engineering company and instead wants to do it in the future (good for him!!!), so you need to put it in the future tense (example: he will take, he will be) instead of in the continuous tense (example: he is taking, he is being).

If I am wrong and you are trying to say that your friend is currently taking part in this engineering company, the sentence needs to be adjusted for clarity. You could put the sentence in chronological order with the present tense first and the continuous tense second. For example: "He takes part in one of the biggest engineering companies in Russia and is planning to be successful in the future." I hope this makes sense!!

He helps me willingly and he gives worthywhile advice to me.

"Worthy" is a synonym for "deserving," and it describes something that deserves something else. "Worthwhile" is a word that describes something that has a lot of worth.

On the other hand he could be described perhaps as a bit of judgemental.

Lastly I appreciate that we couldan be in touch with him despite our distance.

You can also say "Lastly, I appreciate that I can keep in touch with him despite our distance."

We dohave not grown apart from each other.

I am assuming that you're trying to say since you have met and into the present, you and Ilia have not grown apart. In this case, the perfect tense (for example: "we have not," "he has not," etc.) is very appropriate :)

Our calls via Skype isare full of jokes, fun stories, and also sensitive topics.