Crack running length of concrete in living room. Should I be concerned?

It's not uncommon for cracks to develop in concrete floors over time, especially in older homes. If the crack is narrow and doesn't seem to be causing structural issues, you can often repair it with a concrete crack filler or sealant. However, if you're concerned about its stability or if it widens over time, it's a good idea to consult with a professional contractor or structural engineer to assess the situation and recommend appropriate repairs. Good luck

I would get it looked at, as you said, your house is only 40 years old.

Hi there yes it’s common to have cracks in old concrete because it fully cures after 50 years you can fill it with grout to prevent and more cracks kind regards axel .

It is common for concrete to have small hairline cracks, these will not effect structural integrity. It’s when these hairline cracks develop into bigger cracks, then there is reason for concern. Concrete can take long amounts of time to fully cure to 100% strength depending on what type, and as your house is only 40 years old this may be the case. If it is too narrow to fit a penny then this should be fine, but if it develops bigger then there could be concern. For now this can be filled with grout or crack filler and should be fine.