These engines typically last well past 300k assuming there's no issues. Oil on the plugs would be an issue though, did you really mean coolant? Usually bad head gaskets mean coolant gets where it shouldn't be like inside the cylinders or in the oil, because it's under pressure when heated up.

As for the not starting, there's not enough info in your post to figure that out.

Does it spin over but not fire? Does it not spin over? If not does the lights dim or go out when trying to start? Does it start with a jump? What's the voltage of the battery with it running and not running? Is the dash battery light on?