Notwithstanding this part and part 2 of this chapter to the contrary, no municipality or regional planning commission shall adopt any plan, ordinance or rule which would require a subdivider, whose proposed subdivision is outside the corporate limits of any municipality located within the regional planning district, to install curbs, gutters, or sidewalks, unless both public water and sewage systems are to be made available within eighteen (18) months after the subdivider requests approval of the subdivider’s plan of subdivision. This section shall not apply to counties having the following populations according to the 1970 federal census or any subsequent federal census:

or to counties with a metropolitan form of government.