You should attach the graph with your essay.
a period 100 years
a period of 100 years
The countries who included in this survey are Japan, Sweden, and USA.
This sentence could be merged with the previous one:
The given graph shows the proportion of elderly population during a period of 100 years in three different countries, namely Japan, Sweden, and the USA.
increasingly resemble
follow a similar upward trend
the number of elderly people
the proportion/the percentage of
in 60 years appeared
This is not clear. Do you mean "the first 60 years of the period"?
the trend will developing sharply until gain the highest percentage than others in 2040.
It continues to rise until reaching an estimation of ... in 2040, which is significantly higher than the other two countries.
other trends reveal that the elderly population either Sweden or USA were quite similar
The elderly population in Sweden and the USA experienced an increase during the course.
Both of trends
Both figures
Therefore
This world should be omitted.
.