Slower but not worse?

I am not sure about elephants, but recent work at Tübingen University in Germany claims that older people do not decline mentally with age, it just takes them longer to recall facts because they have more information in their brains. Akin to how a computer struggles as the hard drive gets full up, humans just take longer to access information. The researchers say this slowing down it is not the same as cognitive decline. Time to defrag the old brain?