Listed benefits of youth migration:
Long term tax base
Population subsidy in the form of new citizens in the prime childbirth rates
Supplementing 1. and 2. couples or singles who have a child in the region will quickly form lifelong ties, creating a futher expanding tax base
Increase in overall productivity and supplement to social safety nets.
I could go on but the list is quite long, as i mentioned before highly skilled youth immigration is an economists dream.
For a short term subsidy the state gains a long term, high value addition to its tax base along with all the parallel benefits.
As i've also mentioned, while this is great for the destination country, the loss of highly skilled young people could quite quickly lead to negative economic outcomes for the originally hosting country.
That said, I was only thinking on the government level, i hadn't even considered that companies could easily have their own "head-hunting" spree and the cost of subsidization could be tapered from the government through companies, enriching both the local economy and the tax base simultaneously.