Hi, your essay failed to reach 150 words, however with only one line in the graph it's difficult to write more than that! I suggest you to move the last sentence just after the introduction and to join it with the overview.
As can be seen from the chart, the amount of young people in the Uk who choose to eat a vegetarian diet increased gradually from 1960 to 2020.
I don't think you should use the past. You could say, for example: During this period of time, the proportion of UK teenagers who decided to follow a vegetarian diet increases.
Hope you find it useful.