However there are many studies in modern times that would verify my statement but I'd like to go with my personal experience on it.

You know I'm from India and it's a land of Yogis who have committed their lives to Yoga. I've never met an yogi, old or young, having any sort of lack of memory or the diseases you mentioned above. It's an evidence in itself how much Yoga is helpful to eradicate dementia or memory loss. I'd suggest you to try it and see by yourself.

Here's one article that supports Yoga