Older homes sometimes need to have plumbing and electrical upgrades done just so that they are compatible with modern living. That can be a factor in pricing. Another is something called functional obsolences, small rooms and closets, very low ceilings, small kitchens, one bathroom, lots of narrow hall ways. That can also be a factor. On the other hand, if a home has good bones, or has had a recent remodel, the actual age of the home may be less important. It is like they say, the most important 3 things are Location, location, location.
There are lots of things that go in to pricing a home. The best way to determine value is with a good realtor, and a good home inspector. If you are a buyer, and considering an older home, just be sure to do your Due Diligence and make sure your eyes are wide open.