I tried staining a recently sanded 60 year old oak floor and it was a disaster. As old wood ages, it naturally gets darker. Some pieces are darker than others.
Ultimately I decided to resand and go with a clear varathane. Results: nice golden oak color (almost a maple color!), with slight variations between each floor board. It matches the wainscoating really well.
I wouldn't stain OLD wood, but I would stan new wood only dont go overboard. Use a warm stain color or the house will look dark and gloomy.