Why become Japanese ?

[undrentide]

Out of interest, how differently did people write back then?

Not so big difference, but the style could be more formal.

What made me think that he can be an elderly person is only two words.
同じ目に合わしたい cannot tell why, but 合わしたい instead of 合わせたい sounds like... oldman-ish for me.
And 東京帝国大学 is definitely a term used only by the people who knows the university before 1947.

Other part of the message is rather unnatural for a native, but at the same time has something hinting that the poster himself or someone who helped the poster is someone who spoke Japanese long time ago.