Bastian, you have a good potential to write an outstanding a piece of writing. I like the way you present the data, it is very clear and informative. However, amidst all of that, I think you still need a few works on your grammatical errors regarding to this essay. Then, my suggestion is also related on the use of your range of vocabularies. I reckon that you need more efforts to do that, try to reduce some repetitive in your essay. By doing that, it is possible for you to make you pass the IELTS test with flying colors. Now, for a breakdown of some grammatical corrections.
chart
chart is only for bar and pie. Line usually 'Line Graph'
it can be seen that despite
it can be seen that, despite... (comma is necessary)
Aged 44-45 and 34-44
For people in the age group between 44-45 and 34-44, they were...
There were slight decline in 2000 for both categories
2000 experienced a slight decline for both categories.
form
from
two age group
two age groups
aged 44-54 and 33% for aged 34-44.
people between the age group of 44-55 and 34-44, at roughly 33%
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