Well, believe it or not, the age of starting to lose what you have learned, doesn't come for quite a bit....like someone in their 90's, per se.

However, the knowledge you have gained is stored in the deep recesses of your brain, laying dormant, because you have no real need for it. You will notice that you are not using a lot of what you learned in school, unless you were a college graduate, who entered a business and presently still work it.
I am 41 years old and I'm presently proud of what I have gained over the last 10 years of my life. It's taken a lot of weigh off my shoulders, weigh I was applying to myself, even though I didn't know I was. It's really weird to explain what I've been going through. My awareness is like a well cut diamond.
Sorry to ramble. 