If you are good at managing finances and know your way around the financial world, then you can start with an online casino at any time. But it is best that you start an online casino when you have enough knowledge and experience in the casino business. Resist the temptation of starting an online casino when you are new to the business.You need capital to start an online casino. The only way to raise capital is to go to the banks or venture capitalists, but for this you need a business plan and a detailed description of how you want your online casino to work. It is good to have worked in the casino industry or be a player before starting your own online casino.
You responded to title question. Basically never start an online casino if you don't have half a milli $ to start with.