Like Frakke, I started with a board & buggy in 2001 (yes, another life-begins-at-40 pastime). Having skated back in the 70's and snowboarded for over a decade, boarding seemed like the natural progression for me (the Blade/Frenzy route) until a serious, permanent ankle injury put my partly airborne boarding days to an end.
Personally, I enjoyed both disciplines regardless of expertise (or lack thereof). However, on returning to the sport about 18 months later, buggying was the only practical option ...... but I'm as happy as pig in sh*t to still be flying kites
So, is buggy vs boarding an age thing?
Well, boarding could be regarded as a little more 'hip & trendy' to some (possibly younger folks with small cars). Others, with less of a natural sense of balance (possibly older folks with people carriers / estates) might feel more comfortable with the natural 'riding a tricycle' style of buggies. It's hard to generalise, but one thing is certain ....... when your legs / knees / feet & back start to fail then the attraction & practicality of the 'mobile commode' does grow stronger
IMO, the bigger age-related factor is the style of kiting rather than the mode of traction. In general, older kiters are more likely to have more responsibilities than a single, unemployed young student, so older folks (myself included) might veer away from freestyle disciplines (think Frenzy/Blades) to minimize risk of serious injury and any related consequences (like retaining your job). Yes, the sport by it's very nature attracts a degree of risk, but cruising or power-sliding on a board/buggy (think Access/Bullet) carries a relatively lower chance of injury .... on average.
As for racing, on the surface this does seem to attract folks who are out of their teens (yes, there are exceptions where parents & children both race). Maybe this is because older participants tend to have more disposable income, a bigger car/van for transporting kit, and are possibly closer to having a mid-life crisis than your average spotty teenager