Eight is a little old for true (idiopathic) epilepsy. It usually strikes young adults between 1-5 years old.
Did your vet run tests on him? A complete blood panel? A thyroid panel? Thyroid imbalances can cause seizures.
Here is a list of possible causes of seizures in dogs over five.
FIVE YEARS OF AGE or OLDER
Neoplasia: Primary; Metastatic
Metabolic:
Thyroid dysfunction; Hypoglycemia - insulinoma; Hepatic - cirrhosis; Electrolyte disturbances
Vascular:
Focal ischemia - Thromboembolism; vasospasm
Hemorrhage: hypertension; vasculitis
Inflammatory:
Infectious - Viral: canine distemper; parasitic; bacterial; fungal
Immune mediated
Primary: Idiopathic Epilepsy ("idiopathic" = cause unknown or undetermined)
Degenerative
Toxic: Lead; Drug related; Other exposures
There is a ton of information on this website.
Canine epilepsy and diseases that cause seizures in dogs