I believe this question relates to AP Human Geography, so i’ll be using my knowledge from that class. With a large base mean in a country, it would mean that as they get older there would be a large laboring class. This large group would also most likely make an increase in the crude birth rate, increasing a countries population. Then as they reach the age of 60+ they would be very dependent of the younger generations to help them, and also create an increase in the crude death rate as their generation starts dying. Hopefully this applies to your question, I took this class a bit ago so I may be a bit rusty.