The common causes of seizures in old patients are cerebrovascular disease, dementia, gliomas, meningiomas, vasculitis, hypertensive encephalopathy etc. Investigations like EEG, carotid and basilar artery ultrasound, orthostatic blood pressure measurement and routine biochemical and hematological screening can help differentiate between possible underlying causes. Seeing a neurologist for correct diagnosis and management of his condition is very important. Treatment will depend on the cause. I hope it helps.
Best luck and regards!