So the article claims that people can improve, and improvement is necessarily based on surpassing prior, personal ability, and you’re mad?

I didn’t see anywhere that they said that a 90 year old can get the brain of a 20 year old, only that it can still be improved at that age and we don’t need to resign ourselves to a degraded mind when we’re old. If we buy a new car it’ll never be as clean as it was off the lot, but that doesn’t mean it can’t at least be repaired and kept roadworthy later into it’s life.