Good grief.
A 24 hour period is applied to the time it takes the planet to orbit the sun. As both are slowing down, days are getting longer. Don't worry, you won't notice.
Brain activity and development increases upwards until around the mid thirties although that has not been set as a limit, just a guide. If you want to refer to the physical size of the brain as an indication of the amount of knowledge stored, then that is a different matter, and you would be wrong. The capacity of the brain is far greater than most, if not all of us, would ever need or use. And, actually, it has been shown that the size of the human brain has increased through evolution driven by, as one factor at least, the increase in available knowledge.
The phrase "multiply in size" may not fit with what you are trying argue but, that is not what I said in the first place and, is irrelevant to my original argument so, I don't feel any compulsion to discuss it further.
And, yes, I do know what exponential means. That's why I used it.