ANSWER:

The line chart graph shows the percentage of the elder population over 65 years old in 3 different countries USA, Sweden and Japan in whole 100 years from 1940 to 2040. For example the proportion in Japan form the least to the most. (The question said over 65 years old deliberately. It does not use the word elderly because elderly is defined differently in different countries with different ages. Writing 'aged over 65' is precise and clear to the reader. Keep using it through the article.)

With the beginning In 1940, 5% of Japan's population had were aged over 65. is only 5% old people in the whole country's population,also For the USA, it was is almost 9%, and in Sweden, the figure was just between them is at 7%. (For an answer like this, it is better to use the years in numbers. Keep using the past tense)

20 years later In 1960., the figure in Japan had dropped to approximately the old people who lives in Japan are become less, is only 3%. But for USA and Sweden, the figure increased to approximately 15% in both countries to until 1980.

in lastly few years of 20 century, From 1980 to 2000, USA and Sweden got the some number about the old people's percentage roughly followed a similar course.  And Japan are always under the 5% until 21 century .almost in 2005 it's back to 1940's 5%. In Japan, the percentage stayed under 5% until 2005 when it reached 5% again.

And In 2010 the old people in Sweden, the population aged 65 and over are were 20% of the population. In By 2030, those the 3 countries all are were all the same percentage at around approximately 20%.

Finally, in final 2040, Japan got the most elder people had the greatest proportion of aged over 65 ,the number with a figure of just over 25%.