"In the deciding battle for the mainland, the Britannian forces introduced the humanoid autonomous battle armoured knight known as the Knightmare Frame into actual combat." — DVD subtitles

"In the deciding battle for the mainland, Britannian forces introduced into combat the humanoid autonomous armoured knight, known as the Knightmare Frame." — English dub

Surprise! We just unveiled giant robots that can shoot you.

Marianne Lamperouge's history and the development of Knightmare Frames are difficult for me to reconcile, despite having watched this thing eight times, read and watched much of the C-canon (picture dramas, most of the novels, DVD booklets), and even a lot of the S-canon (manga that in a few places didn't directly contradict the show). The Code Geass Wiki has also been helpful, reminding me of things I've forgotten and telling me things that I never knew.

Basically, this is my problem: If Knightmare Frames were introduced into actual combat in 2010, how could Marianne vi Britannia have been a hotshot knightmare pilot in 2009 and earlier?

I guess that Britannia used more conventional means to conquer Areas 1 through 10, and I realise that the Knightmare Frame did not become a weapon in its earliest generations, but the Knights of the Round seem to have been around first, and Marianne definitely duelled Waldstein before her untimely death. If, indeed, she was in the Knights of the Round when she met Charles, for how many of the eleven or more years before the Second Pacific War did she test-pilot the third-generation Ganymede? And if these machines used by the most honoured knights of this world-conquering nation were used in an assault for the first time in Japan, I wonder if the first ten hard-fought wars could have been made a lot easier.

That said, I don't recall seeing any weapons on the Ganymede that weren't put there by some Einstein, so could all of Marianne's Knight of Sixiness and duelling been without Knightmare Frames? After all, I did see her with a horse in the flashback in R2e21.

Please correct anything I've misstated. If you can shed any more light on this, I'd be appreciative!

Edit: Here is what I have learnt in the comments to this post.
unedited: "Marianne was awarded knighthood because of her skill piloting the third-generation prototype Ganymede."
otakukeith: "It seems to be established that she was a badass hand-to-hand fighter - in the novels, she dual-wields swords, kills the former Knight of One in single combat during a rebellion against Charles, and can beat Cornelia, Nonette and Beatrice (a character who I think was a failed KoR candidate and became their liason officer thingy) by herself."

Does any character's age (e.g. Lelouch, C.C., Euphemia, Tianzi) have a bearing on your enjoyment of Code Geass? Positive or negative?