Recently purchased for my 4.5 year (the "mini" version, while a little lighter hasn't got the longevity of use this one offers), he loves it and as other post comments, 6+ age I suspect is to encourage parents to wastefully purchase the "mini" (which is fine for 2-4 years in my opinion); zips along with his bicycle helmet on, spends more time outside on the weekend than in now and it's good exercise for him and me trying to keep up.
Extremely stable and very high quality build.
Only negative: More expensive than some alternates, but you try getting one of these secondhand!