I love old houses but there are some things to consider when you look it over.
Are there a lot of electrical outlets? Many old homes have like one outlet per room. If your ok with that then fine.
Walk the floors, especially on multiple stories and have someone else (hubby) on the floor beneath when you do. Many old house squeak like crazy. You might not notice it when you looking it over, but you will notice it when you move in.
Most of the time it isn't a problem, even a little squeaking, but you might not care for it if it is loud enough to wake you up for example.
Keep a keen eye out for previous leaking. An old house is bound to have had a leak at one point or another, just make sure it looks like it was temporary.
If it has a well, make sure you have it tested. Nothing worse than a shallow well that goes dry if you wash too many dishes.
Check for dampness in the basement/cellar. Check for musty smells, etc..
Flush the toilet a couple times and see how fast it drains. A slow draining toilet may indicate a problem with the septic.
If it is furnished, look behind furniture, under throw rugs, etc.. Homeowners will hide many things this way.
Old houses have a tendency to have small doorways, and low ceilings. Make sure that your ok with it if that is the case with this house.
That is all I can think of off the top of my head. I have lived in many an old house.