I see loads of over 80's with back problems. As has already been said, think of the age and other problems and are there any "red flags"?. Has the person had an x-ray /Wikipedia reference-linkmri or anything to rule out massive degenerate change, osteoporosis, spontaneous fractures, stenosis etc?
If possible serious pathologies are ruled out, as far as one can do, treat as a back problem but cautious in comparison to clients much younger. Ergonomics in every day lifting /sitting habits should be looked at. If OA hips and knees prevent sensible lifting it is difficult to calm down a back problem. Feet deformities and bad gait also affects the back.
As far as exercise goes, it depends on what sort of 80 year old you have, some have been active all their lives and some not. If there is an accompanying muscle imbalance problem it's usually possible to do transversus training and indeed lots more, even in older patients it's possible to help weakness of muscle.