Just To Point That GRU Never Was Part Of KGB (that Is A Separation Which I Want To Made Patent In My

Just to point that GRU never was part of KGB (that is a separation which i want to made patent in my book). GRU is military intelligence, it is around since 1918 and by the name since 1942 and is still active (kinda SEAL team 6). KGB on the other hand is just civil intelligence (much like CIA) with both national (KGB) and international (SVR) reach. Anyway, cause the Red Room project she can be a full fledged agent at age of 9.

The problem I have with Natasha being born in 84/a full fledged KGB agent is that the MCU follows real-world history relatively closely. The Soviet Union collapsed in '91. If she was born in 84, there's actually no way she could have been a full-fledged KGB agent. It's just not possible. She could potentially be SVR RF or GRU (most likely GRU), but it just isn't possible for her to have been KGB at the age of 7.

I’m not going to say it could never happen, but I do doubt it. The screenwriters for CA:TWS (and CA:CW and A:IW) were asked a question about Natasha’s age before CA:TWS came out:

The comics obviously have this history between Winter Soldier and Black Widow, although Black Widow, as far as we know, was not born in WWII. Was there a different way you could approach that dynamic between them?

CM: They have crossed paths.SM: Yeah, we will leave it at that. But yeah, we acknowledge all of that stuff. We get it, but it’s—CM: Then you wind up in Infinity Formula territory where everyone is a 100 years old. That’s a strange world. [X]

So I really do doubt that Natasha is going to turn out to be secretly older. Which brings me to your point about the KGB. I think there is an easy explanation for why she said KGB.

Ease of storytelling.

Listen I’m a history nerd so this annoys me too, but what it boils down to is this: if you say “KGB” audiences around the world know instantly who you are talking about. And more importantly, audiences of English-language popular culture know that the KGB are the “bad guys”. If Natasha had sat there and said GRU, the vast majority of the audience would have no idea what she was talking about, and they would have had to extend the scene for her to explain to Steve (and the audience) what that was which would have A. increased the running time and B. dampen the emotional punch of her line. So from a storytelling pov, it makes perfect sense to use the KGB even when it makes no historical sense at all. 

I think that if we ever get some sort of explanation for her line in the future, it is much more likely that the filmmakers would explain it one of two ways:

the MCU’s KGB continue on after the dissolution of the Soviet Union, and never split into the GRU and the SVR RF like in our world

Parts of the KGB - like Department X - went underground either after the failed August coup or when the Belavezha Accords was signed.

Either explanation could work and the difference between our world and the MCU could easily (and conveniently) be explained/blamed on HYDRA manipulating events from the shadows.