Depends on what you actually have there. Some very old systems were what they call cesspools. That is nothing more than a pit that has a pipe coming from the house and everything goes in there, liquids and solids. Some were laid up with stone, or cinder blocks. I have even seen a metal tank buried that someone just drilled holes in! Cesspools are the worst of all the systems. They were never designed to handle today's water consumption (dishwashers/washing machines and 10 minute showers). They fail all the time. Especially when tested by a home inspector. There is no drain field, it's just a pit. all the contents stay in there until they drain into the ground.
Another system is a septic tank and drain field. Both liquid and solids go in the tank but once the level reaches a certain point, the liquids leech out into perforated pipes that evenly distribute the liquid waste into the drain field. Then it filters through the ground. The solids(and some liquid) stay in the tank and need to be pumped out every few years. These can fail also when the the drain field becomes saturated and will not absorb any more. A die test can be done to see where the drain field is. A hydraulic load test can be done to see if it's saturated. Usually the tank is not the issue unless it has a crack or is otherwise broken.
I assume it's not an elevated sand mound as those have only been around (in my area at least) for about 30 years. They too can fail for some of the same reasons.
Investing in areas with on site septic systems (anything other than public sewer) can be very risky. If a system takes a s*** (PUN INTENDED), it's a MAJOR expense. There are some techniques to help but they only buy you time. Eventually the system needs to be replaced. The real trouble comes when the ground is not suitable for a new system either because of the lot size or soil conditions.
I say have a professional test done to be safe and use common sense. If it's a very old house with a cesspool, would be inclined to walk unless it's a screaming hot deal!