I wait a month in between 5 day fasts. The benefits of fasting come during the feeding stage. During this time I try to only eat whole food that I prepare myself and I focus on nutrients. I don’t have a lot of excess body weight. I also like to workout and be active which I can’t do on extended fasts. A month seems to be the sweet spot for me.
I’m not a doctor but I personally see no issue. Listen to your body, but if you have a significant amount of fat reserves for the body to utilize- I say it’s open season. Do some research on ketoacidosis and potential measures to avoid it would be my last thought.