How humans store information?

I often wonder how much is known about how humans store information and how we deal with different types of information. Obviously I only have my own brain for reference.

70 years old now and have noticed a steady but slight decline in my ability to recall words and factual information. I actually think this started at about the age of 40. My ability to stay with something until I grasp it has somewhat improved with age so that helps out a lot.

I wonder, is all the information from the past still in the brain but we are just unable to recall it? Or has a lot of it actually been erased?