Kids who were kept on such diets, would normally transition to normal diets, they apparently either outgrow epilepsy or can take drugs to control it once they get older. None of the kids preferred to stay on it for life either, I've been told (altho that neuro's sample would be small), it is quite burdensome.
Encouragingly, many mountain tribes eat primarily meat/fat based diet, and the same goes for Inuit tribes in the Arctic. They eat such diets for their entire life, and mountain tribes often have quite long lifespans on primarily sheep meat/fat and some greens. a little bread/starch every now and then.
So maybe it is safe for some period of time. It is not clear what health risks you accept as trade-off, nothing is free.
Intermittent fasting on the other hand is extremely safe and is privately practised by several physicians I trust. They all seem to be in great shape for their age, fwiw.
And yeah, I'm using intermittent fasting too. Happens quite naturally and I guess that plus evening runs around the block really burn those calories.
Long answer (this is not medical advice): certain risk groups (related to kidney and liver function) should not observe a keto diet without consulting with their doctor. The long term risks of an animal protein heavy keto diet are unknown (think colorectal cancer from red and processed meats, including those with nitrates used in their production). Be mindful of electrolyte and water consumption while on a keto diet.