Learn English – It’s been ages vs You’ve been ages

you've requested is a relative clause in which the relative pronoun has been omitted (or, if you feel fancy, has been replaced by the null relativizer), which is permitted because it represents the object of the clause's verb. It is equivalent to that you've requested or which you've requested.

Simple past you requested is more usual, but the present perfect is unexceptionable: although it is true that you made the request in the past, it is obviously still relevant today, and there is no time marker such as requested last week which would require use of the simple past.

No distinctive meaning is apparent in this use of the present perfect. I think it is innocent pomposity.

In answer to many requests, it was decided to extended the paper submission.

What you have there is just patently wrong. We're talking about the basics of English grammar here. You can't have the past tense form (or past participle for that matter) of a verb be part of the infinitive form of that verb. They're mutually exclusive, if you will. It should be to extend, of course. The reason why is because in English a verb that follows the main verb in a sentence or clause must be put in infinitive form. This rule breaks in certain, though very rare, circumstances. For example, most people instead of saying I'm gonna go to check on the dinner will say I'm gonna go check on the dinner. Notice, there is no to between go and check.

"The paper submission was extended". Then the "extended" word is used correctly. Am I right?

Yes, you're absolutely right. That's because was extended is something grammarians call a passive voice. It is formed by following any of the conjugated forms of the verb to be with the past participle of the verb that you're using.