Spoiler: WW2 happens and Kagami dies.

Natalya said the Russo-Japanese war happened "a few years ago", so we're probably around 1909 right now. If Kagami is 18, then she was born in 1881, which seems to fit with her age during her flashback (assuming that was during the same war). That would mean she joined the academy just 2-3 years after. I think that WWI happening is more likely, possibly after a timeskip.

Side note: have we seen a single second-year or a mention of one existing yet?