To get rid of an old house smell you can wipe down the walls using the following.
Create a cleaning solution to clean your walls with by mixing together two cups of vinegar, one cup of borax and 16 ounces of hydrogen peroxide bleach in a bucket of hot water.
Then wash your walls using a sponge or rag or mop but don't get the walls too wet as that can cause mold growth but you just want to clean off the walls to help get rid of any odors that the walls may have on it.
When you wipe the mixture over your smelly walls it helps to break down grease, kill mildew and get rid of old house smells.
Also using an air purifier and opening some windows on nice days to help the house air out can help with the old house smell.
Get rid of any old carpet or at least use a carpet cleaning machine with some vinegar or sprinkle baking soda onto the carpet and let it sit for a few days.
The baking soda helps absorb the odors in the carpet.
Old house smells are usually caused by high humidity or damp conditions so you need to keep the humidity level down and get rid of any damp conditions to help get rid of and prevent old house smells.
Using a dehumidifier and your air conditioner on high humidity days help with getting rid of the old house smell as well.
Or even just placing a few boxes of baking soda around the house can help absorb odors as well.
Just open the baking soda and leave it sit on a counter, shelf etc so that the baking soda can absorb the odor and have your windows open as much as possible to get the odors out and bring fresher air in.