There is no rule hidden somewhere that an expert can retrieve and share with you. The acceptable rate of growth is what you accept until you have bosses or owners or investors that establish something else. Industry overall grows about the same rate as the economy, which is 2-3% in a good year.

It's only the outside forces, like investors or banks, that demand certain growth rates. If you own it yourself, you demand that growth of yourself. By the way, 20 percent+ is outstanding growth, 7-8 percent per year is higher than average.