If the propensity of younger people to move outside their home locations has decreased that's interesting...if not necessarily a bad thing. But I don't think it has much to do with younger people being less likely to get driver's licenses early, except to the extent that some of those people aren't likely to move out of more transit-friendly locations.
To much for the margin of this blog post, but I do think The Internets have worked against all kinds of geographic mobility in counterintuitive ways. I'm just not sure that's a bad thing.
