NorthGrim

yes

I like the start I think it has potential, all I'm wondering now is if you dropped it or not.

He grew to be 181cm by the time of a thousand year blood war so by age 17,18 he's 5'11½

The name of the manga is "Burn the Witch" it's spin off of bleach, I think it might have an anime adaptation.

Well there's a manga in the same world as bleach , only taking place in europe and they have witches and dragons so could happen.

Him knowing about it doesn't mean he remembers all of it and he read the light novel up to a certain point, dropped it the years before he died, then he lived about 17 years and then got his memories back.I'm guessing, it's abit foggy of things that happened in the light novel.

It's from another novel with are similar concept of upgrade. The whole power armor exchange is basically a word for word of that novel.

So he was born in this world

He didn't it's still in pending, he still has to choose yes or no.