The two countries I selected are Japan and South Korea

Japan:

Males per  100  females:  93.9

People per kilometer:  345.3

Number of children per woman:  1.4

Current population:  125.9  million

Estimated population in  2050:  107.2  million

South Korea:

Males per  100  females:  100.4

People per kilometer:  532.8

Number of children per woman:  1.3

Current population:  51.6  million

Estimated population in  2050:  47.7  million

Japan has a slightly larger female population  than  South Korea's which you can see on the pyramid because there's more on the right side.  Both pyramids are larger in the middle from people in their early thirties to late sixties.  There are way more people that are 30+ than young people in both countries. It appears that the birth rate began to lower drastically about 30-40 years ago. This explains why the population in both countries will start to lower  drastically within the next 10 years. By 2050, both countries will experience a large   population decrease due to  the die of the older generations. This makes sense  because the two largest age groups  in  Japan according to the pyramid are adults in their late 40s and late 60s.  Unless the birth rate increases dramatically within the next 30 years there will be a large population decrease.