Raised horizontal lines along walls throughout house
I'm afraid the age of the house can not be blamed for the drywall seams  being noticeable. Dry wall seams, when completed properly, should be invisible even under close scrutiny.
It sounds as if only 1 or 2 coats of joint compound was applied. The solution is to apply more compound in wider passes to ease the compound to the surrounding wall (Feathering). 1 or 2 more coats should blend it enough to be unnoticeable.