"30 years" is factually incorrect. The requirement is to be a permanent resident for 5 years (I can find links if needed). Source: I'm currently awaiting my naturalization appointment, if all goes well the total time from setting my foot in the US to becoming a citizen will be few months short of 9 years (~2.5 years on work visa & 5 years on green card + ~1.5 years wait for naturalization appointment).