Tom Vanderbilt links to an article in Ad Age about the decline in drivers licenses among youth between 1978 and 2008 in the US. This data surprises me, not just the decline in youth licenses, which can be explained as Tom notes by graduated driver's licensing programs, but a decline between 1998 and 2008 for all drivers by age group, which is shown at the bottom of the Ad Age article according to USDOT. While I know auto ownership peaked in the past few years (with a decline in total cars last year), and the recession and high gas prices have changed patterns in the past half decade, this is remarkable if true.
I retain some skepticism about whether this is instead explained by a switch to other forms of IDs among non-drivers, (i.e. in the past a DL was considered standard ID, so people got that from the DMV even if they did not drive) or some sort of other accounting issue.