Anecdotal, but I'm well past 30, and I notice a marked improvement in cognition when I have a small, high-protein breakfast. Granted, I'm on a portion-control, no-processed-food diet the rest of the day too, so I'm rarely ever consuming more than I need.
Right, portion control requires a lot of discipline. I choose to have fewer meals instead :)
It's easy to overeat even with just two meals per day.
As for better cognitive facilities - I feel like a lot of that also can be achieved with being disciplined about sleep and getting enough of it. Nothing can really replace it.