Two patients can be the same age on paper and have very different brains.
Modern measurement lets me estimate the age a brain appears to be, based on its structure, and compare it to the age the patient actually is. A healthy thirty five year old can carry a brain that looks closer to twenty six. Someone doing the right things for their body earns that.
The finding I care about most is the drop. A person whose brain once sat near the top of the curve, who has fallen to merely average.
Almost everyone misses this, because average does not look alarming. But going from exceptional to ordinary in a short span is not how a brain is supposed to age.
That decline tells a story a single measurement never could. It is not where the brain sits. It is how far it has traveled to get there.
The most useful reading is often the one that notices the distance fallen.