From meeting many of our customers over the past 18 months or so, I've been pleasantly surprised at the age range. Many are in the 30-50 bracket, which is at odds with the perception that the hobby is mainly the preserve of the older generation.
As Fran said, Marklin's kids' sets are among the most popular toys in Germany. They're also compatible with the regular Marklin sets, which helps promotes quality parent/child time, too, as well as nurturing interest in the hobby. There's a distinct lack of an equivalent product in the OO market...
On a related note, there's very little promotion of the hobby towards people who don't already have an interest in railways, certainly here and in the UK...