A few kg of blueberries a day? All my food for one day together weighs less than that. Did you mean grams? That seems low, but kg/week is still way too high.
Blueberries consist mostly of water(proteins, carbs and fat make total of 7.5 grams per 100 grams, more or less rest is water), so they aren't very rich in calories(44 kcal per 100 grams). Of course all sorts of berries would rather be an supplement than a primary energy source in the first place.
But indeed, kilograms per day? Sounds too much to be optimal, and relevancy for aging or combating it from perspective of brain development is totally left out, which makes the whole claim even more astounding. Sources or gtfo! :)
It's quite easy to eat a lot of berries in one go - I can manage 454g of strawberries in a sitting, no problem - but I still think more than kilo or two of blueberries would be a tall order.
Besides, think of the cost! Here are some US prices, as best I can tell. Anywhere from $20/72oz - i.e., $9.80/kg!
From what I've seen, my own father and grandfather is still sharp as a razor, easily faster than most guys my age and far wiser.
For now, eat a few kg of blueberries everyday and take some alpha lipoic acid. Also, donate to anti-aging research if you have the money.