Ct scan result -brain and posterior fossa demonstrate age related volume loss. is normal?

Eye of Beholder: The "eye ball" observation of "volume loss for age" is extremely subjective with much intra and interobserver variation. That means readers often don't agree and are sometimes not even consistent when the same reader re-examines an image twice. Computer programs are being developed to analyse brain volumes accurately and precisely but are not in general clinical use yet. My advice, don't sweat it.