Older houses are at greater risk of having mold infestations then relatively new houses. In studies that we conducted in Australia, houses greater than 20 years of age had significantly higher airborne mold levels. The reason for this is that with the passage of time there is an increasing probability that some thing will happen to cause a mold infestation problem. This may include plumbing failures, high humiditys in basements, storm damage, etc. Nature is not kind to houses.
Humans have to work at it to keep the forces of nature at bay.
One hundred year- old houses have many owners or tenants. Even a week of neglect is enough to cause a major mold infestation problem. Check your basement for any signs of mold. If your furnace is in a musty basement, mold spores will be carried upstairs in a matter of seconds every time the furnace comes on. There are no test kits available that can be reliably used by homeowners to test their own homes.