I only looked at donepezil MMSE charts for mild to moderate Alzheimer's. The charts for severe Alzheimer's are obvious, because they decline very quickly regardless of the treatment. If I had looked at severe Alzheimer's charts, it would hurt donepezil compared to 2-73.
I'd have to look at the ages. They are multiple studies. Still, I wouldn't extrapolate from differences in age. I don't know enough/haven't studied enough to reliably be able to say how age would impact the drug's effect on MMSE.