You could probably consider the British royal family a business.

But even if you don’t do that, for a long time the British empire was a corporation — the east India company.

Weren’t they just a majority shareholder?

What would you peg as the starting date of that? I think it's not quite that old, although I'm not a historian, so I might be wrong

1707 when Britain became politically united and ceased to be England and Scotland.

The English colonies preceded that, but it was not British. Cromwell's invasion of Ireland was the start of the plantation system, i.e. settler colonies.

Before that there was the brief Anglo-French dual monarchy during the reign of Henry VI.

And before that there was the larger Angevin Empire which included Britain, Ireland, and the western half of France. However I would consider that Norman rather than English as the rulers spoke French.

It wasn't an Empire until well into the Enlightenment. England was not really important at all for the longest time.

QE2 and House of 'Windsor' (heavy quotes) however, can trace their lineage back to the days pre-Norma invasion, so a little over 1K years by that measure.

Because it's a nation, not an asset-holding entity that is nation-agnostic.

The Vatican is a nation.

It is, nominally, a nation in name, done for political reasons to remedy the Italian government's exertion of power over the institution. Idiosyncrasies of naming aside, it serves much the same purpose as a corporate headquarters. And regardless of all of that, it's nationhood is new, under 100 years old. Imagine we suddenly granted Apple headquarters nationhood: it would not change the material reality that it is functionally a corporation.

The Papal States were a thing for about 1000 years though.