There is no set ban frequency, it comes down to how many hours a day you bot, what you bot, and how movement intensive the bot is. If you are using a public script, I would never expect to last more than a few days on a fresh account as Jagex has already likely banned 100's of accounts using the same script and now can detect the movement patterns of that bot in particular. Even if you decide to use a private bot that is movement intensive or is in an already saturated area, your accounts would still not last more than a few days in most circumstances. I would highly recommend searching for a method that is relatively unknown that doesn't require a ton of clicking if you are trying to gold farm and find a highly skilled scripter to make a private script for you. You should in terms of gold farming use multiple proxies that way you aren't botting 50 accounts on one ip which would potentially save you in the case of a chain-ban. With that being said thou, following those steps does not guarantee safety from being banned, it only reduces the risk that will always be present in the botting scene.