I don't think it's far fetched to speculate that the Switch's audience is on average older than that of PS4/Xbone. Kids mostly want to play what their older siblings/peers are playing, hence M-rated games like Call of Duty and GTA being swamped by preteens. At that age, the desire to emulate adulthood is a normal part of the maturation process. To a lot of kids aged, say 10-18, (or even older than 18 in some cases) they want nothing to do with things seen as "kiddy" and only want to play "grownup" stuff, hence they ask their parents for a PS4 or an Xbox One instead of a Switch cos those are seen as the serious systems for grownups.
There comes a time later in the maturation process however where most people realize that trying to be grownup is in fact a trait of adolescence, not maturity, and that grownups play whatever they damn well please, be it E rated or R rated. As such, people who have reached true maturity are more likely to want a Switch than an adolescent.
Look at Switch's advertising; it's primarily geared towards hip urban professionals in their late twenties and thirties. The very design of the system is geared towards adults with a busy work life who need to squeeze in their gaming when they can between their job, looking after kids, etc.
Let us also remember that those who grew up with old school Nintendo in the 80s and 90s are approaching middle age now; the Switch is drawing a lot of these "lapsed" older fans back in by taking franchises like Zelda and 3D Mario back to their roots and providing more attractive hardware that an older fan wouldn't scoff at the way they did with Wii U.
