[tracker1]

You cannot... you learn new things, old things fade. What you can do is maintain and dedicate time to learning things, and/or keeping your older skill refreshed.

About a decade and a half ago, I worked on eLearning systems and training materials. I've learned and forgotten about more things than I could probably think about when trying. I used to know, pretty intently how certain aircraft engines worked, now I'd have a hard time just simply describing how a jet engine works in general.

Why, because I don't use it regularly. I've since worked with other languages, platforms, systems and constantly learn. You will learn and forget a great many things in a lifetime. Most people would be hard pressed to remember as a young adult materials they covered in 5th grade.

What it comes down to is keep reading, learning and trying new things. You won't remember everything, don't even try. What you can do is keep your mind able to think.

As a small aside, avoid refined sugars and seed (vegetable) oils. There are a lot of significant links to dementia and Alzheimers disease aside from being two of the largest causes of inflammation from diet.