A door usually shows symptoms of wear and tear in the areas you hardly notice: the hinges. You only notice that your doors are old enough to repair when the hinges start squeaking. The hinge is a simple yet efficient door hardware which most doors all have in common (except sliding doors), and repairing a squeaking hinge is an easy enough task that even you could do it. Apart from loose screws, lubrication is the usual culprit, so try lubricating the hinges with oil once it squeaks. If the reason for the problem is a screw with loose treads, fill the screw slot with setting filler, let it dry, and then reinstall the hinge.