In "report designer", on your graph, you need to tell it how to sort.
I haven't tried this in 7.4, but this has caused frustration for me in 7.3, so my guess is, it's the same you need to do.
What I do, is press the name of the variable on the graph, select sort and then select ascending/descending.
In your case, you should click on the name "Alder 10-årsklasser" just below you barchart, then a menu should pop up allowing you to select sort -> ascending/descending. It should sort using the custom sort you have made.
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