Jay J is on the right track, here. I just want to say that in some cases, a little "age" is ok. Sure, if you can pass the butter by sliding it down the table, we have a problem. But some old houses are just that, old. And when you try to fix one area, you have to fix another area, which adjoins another area, and so on. Frame houses are usually more forgiving than masonry, at least in my experience. Also, old houses "can" be built quite well with good lumber and framing methods. They can also be made of inadequate lumber and the methods of, shall we say, horse poop. Let us know your situation.
If you have plaster on walls and ceilings, even more problems.......if it is still in good shape. When you start moving things around, it can be damaged. Usually if you live in an old house with "marginal" additions and sagging floors the plaster is gone so you are probably looking at removing it and new gyp board anyway. And...............if you are doing all this, you might as well rewire and plumb and insulate the puppy. (Forgive me, I just get on a role).
My point is, and we will know more when you resubmit with more info, sometimes it is better to "live with" certain problems and fix the major ones unless you planning on a class act restoration.
I am in and out cuz I get busy, but if I can, I will be glad to assist you.