Hi Sepand and welcome to Writefix!

A big thanks to Ngo Duy Quang and to Shieiuan for their comments!

Sepand, you have done a lot of writing around the topic. The ideas are there, but they are very vague and you really need more concrete examples. Your essay would really benefit from being squeezed and tightened until all the empty words and padding drop out.

Word Choice/Word Form/Usage

• People tend to behave with out enough notice to old ones. → People do not pay enough attention to older people.
   
• elderly people must improve their knowledge and ideas about common life → elderly people should improve their knowledge and ideas about daily life/everyday/modern life (???)
   
• it would make some conflicts with new generation and the older one → it would cause some conflict between the new generation and the older one
    
• Older people can be considered highly lucrative resources of experiences → Older people are highly valuable sources of X, Y, and Z. (‘lucrative’ is for business. Unless you are going to boil older people down for their fat, it’s not really right here.)
    
• good traditions and costumes → good traditions and customs

• Definitely, it would make some conflicts with new generation and the older one. →  (Don’t use ‘definitely’ at the start of a sentence in writing. Put it near the main verb).
    
• Actually, spending time with older people is rapidly decreased.  (Don’t use ANY adverbs at the start of a sentence in writing.)

You wrote:

Also they are expected try to act and behave in a flexible way. 

Avoid the passive. Who expects them to try? Avoid the word 'way' - it’s meaningless. Here’s a possible rewrite:

In my opinion, older people need to be more flexible.

You wrote:

If they are not behaved in decent way, the society will be more prone to have not a proper community relationship. (21 words)

Avoid the passive. You can’t behave someone else. Avoid the negative in the second part of the sentence.

If we don't respect old people, there will be problems in our families and in society. (12 words)

You wrote:

Recently, older people usually suffer from deficiency of adequate respect and decency.

The two adverbs are not quite right, the verb tense for ‘suffer’ is not quite right, and ‘deficiency’ is not quite the right choice of word. Here’s one possible rewrite:

In recent years, older people have become less respected and less well-treated.

You wrote:

Teenagers often think their grandparents not only do not appreciate their desires and ambitions, but also cannot understand the circumstance of modern life.

‘Not only… but also’ is BANNED on this website! Seriously, don’t use it. People rarely get it right. Here you are very close, but the two negatives are very confusing. Here’s one possible rewrite:

Many teenagers think that grandparents fail to appreciate their desires and ambitions and do not understand modern life.

Pronoun Reference

In all these sentences, there is a big problem with pronoun reference

• it would make some conflicts with new generation and the older one. 
• Unfortunately, it casts a shadow over good traditions and costumes
• So it causes less attention from children to older people

What does it refer to in each of these? All the sentences need rewriting. Read about Cohesion (how sentences link) in the official descriptors for IELTS Task 2 Writing (public version) and look for the words "inaccurate use of cohesive devices."

Organization

Your intro needs a thesis sentence to tell the reader what is coming in your essay. You can read more about Thesis sentences here.  Another BIG advantage of a thesis sentence is that it forces writers to think about what they are going to say.

 Articles/Plurals

• Older people usually suffer from deficiency of…→  older people usually suffer from a deficiency of...
• New lifestyle has been affected → Our new lifestyle   OR    The modern lifestyle
• it would make some conflicts with new generation → it would cause some conflicts with the new generation
• From psychological point of view → From a psychological point of view
• inthe virtual networks like Facebook → in virtual networks like Facebook
• and new inclination of young  people → and the new inclinations of young  people

Work hard on pronoun reference. From now until your exam, restrain yourself every time you feel the urge to write ‘it.’

Dig out any grammar book and in the chapter about articles. Every singular noun in English needs an article, except for abstract nouns.

Have ideas in order, and don’t circle around an idea. Have a look at the official descriptors for IELTS Task 2 Writing (public version) here, under Cohesion (how sentences and ideas are linked) and under Task Response (how ideas are developed and supported with examples).

I don’t give bands here, for various reasons, but you should be able to find key phrases in the descriptors that will help you to place yourself. Anyone else is welcome to comment and say what band they think it is. What band are you looking for?