Did it always smell like that? Or is this a recent development?
Honestly, if it's the smell I am thinking of (smells a bit like an attic, sort of dusty but not moldy per se, like potpourri that's been sitting in a bowl for a couple of centuries), that's just one of the joys of an old home, along with creative wiring, field mice, and random bits of toys stuck in the floorboards from the previous owners' children.
You can try to get humidity controls in and keep the humidity between 40-60%, because that will help save the wood from getting either wet rot or dry rot. It'll still smell a bit, but not as much. Humidity is a problem this time of year AND in the winter--whenever humidity gets either very high or very low, it's bad for the wood. But given that most old houses have no vapor barriers, it's going to be a constant issue. If you have an air conditioner, replace it with a swamp cooler, that will help keep wood in good condition.
My house smells of many things that I'm sure I never cooked, thousands of wood fires, damp from the well, citrus-scented cleaner, and wet dogs. I decided as long as it is actually clean, I'm not going to bother being embarrassed--if my guests couldn't tell just by looking and listening from outside that the house is elderly and contains fireplaces and dogs, then they aren't observant enough to notice that the second floor smells like a granny's talcum powder.
when I walk in the house and get hit with a weird smell, it usually stems from my husband.
DH always blames the dogs when that happens.