Taking two gap years before Oxford

I second this question, I'm Korean and national service is mandatory... would that go against me if i did it before uni?

Is it possible to take two gap years after sixth form and still get accepted into oxford (specifically to study law)? I’m planning on joining the army (in a foreign country), which would teach me a new language and help me acquire a new skill set, but I wonder how Oxford would view such a thing.

Also, is it possible to apply for university two years in advance, as it would obviously be ideal to apply whilst still in sixth form.

Thanks, any help would be appreciated.