Hire a qualified professional floor finisher to refinish the flooring. It is old growth and ought to clean up very well.

It will have a beautiful creamy - brown aged color that I personally love. Old character will show in what I call bruising where heavy objects where drug across the floor sometime in the past.

Perfect candidate for scraping and waterlox instead of sanding and polyurethane.
Casey

On second look I see the random width boards. Nice floor. Waterlox is an option for you and it will give you good color. The lightest result can be achieved with a commercial quality two-part waterborne (non-yellowing) wood floor polyurethane.

I agree with the bruising comment. Whether you sand or had scrape, expect some of this bruising damage to remain visible. Doesn't necessarily make the floor look bad...it's just the nature of the beast.