well assuming that it is an automatic because of it being an ex, and if the elderly couple when they drove it, didn'tt floor it the whole time which would obviously cause more strain to the engine and transmission, than you will be fine. honda is known for their reliability and endurance.of course if abused anything can go wrong. just keep up the maintenance and you should be fine. the only thing you really have to worry about if you want it to last as long as possible is stay out of the vtec range which has a potential of 290bhp(horsepower of engine off of the car),app. 270hp max,a transmission will not like that very much, much less an automatic.
so to make it easy for you just in case it was to much for you, that accord is a respectable car for its' power and durability. the transmission should be fine unless a recall appears in which the dealership would fix that no charge.