I don't know if this will help you or not but our late great Siamese Solomon was 3 months shy of 22 when he passed on 04, he had seizures from the time he was 2, he was also put on a barbituate, we took him in a few times a year to check weight, and dosage changes if needed.

He took his meds in a bit of liverwurst daily, and the worst that ever happened were some smelly pooters from him.

His personality never changed, he was a smart loving attentive wonderful cat, he is sorely missed , but he died from old age not his medical issues.

Hugs to you and candles will be lit for you all!