How do you clean a 70 year old oak floor?

Here's a good article from This Old House on cleaning wood floors: https://www.thisoldhouse.com/ideas/how-to-clean-wood-floors

This article may help https://www.wikihow.com/Clean-Old-Hardwood-Floors

The finish coat is probably long gone and therefore lots of changes of cleaning solution will be important to keep from re-depositing the dirt and have it sink into the raw wood.

I would use Murphy’s Oil Soap Solution. This is going to be worth your time & money, if the floors don’t have pet stains or other difficult stains.

Pet stains require wood bleach.

Since this Floor is 70 years old, I would tell everyone you want $ for Xmas and it’s for my “Floor Refinishing Piggybank”. Get it professionally sanded and re-urethaned.

I would use ammonia and a scrub brush and then wash with soap and water then give a coat of varnish when done

Try liquid Gold Floor and Cabinet Cleaner!! Value stores