https://kirkegaard.substack.com/p/immigration-economics-for-economist
Anyway, the figure shows the net contribution of some person for a given age based on their modeling (DREAM model). We see that age has a massive effect. Everybody is a net negative person until above mid 25s. This is due to people not working much before this age, but consuming a lot of resources via education and health. In the big middle age, people then repay their 'social debt' by being net positive. This lasts until about age 70, where it is again increasingly net negative until death. People don't work much in retirement, and while they do consume based on their pensions, this is not enough to make up for their very large health costs in old age. Since now everybody survives to every age, one cannot just take a normal integral (area under curve) to get a given person's or group's net value, one has to multiply by survival probabilities.
The differences between the colored lines are obvious and large. The blue line is of course interest as this is the main problem group, and the largest. It's always net negative. There is no age at which this group contributes more to society than it receives. Obviously, this group cannot be a benefit economically to society at any point then, not even if you imported only 30 year olds, and kicked them out at age 60. All the other groups do worse than the natives, which is not surprising because ethnic Danes do well in other countries too. This is just a standard tale of good human capital for this ethnic group. Still, the other groups are at least net positive at some points in their lives, but just not enough.