I'm 35 with two kids, too bad for your ageist argument. (And you don't even need a special kind of bike to carry two kids on a single bike: you can put both a front and back mounted seats on litterally any bike, even foldable ones!)

If the infrastructures are adapted, even carrying 4 children on a single bike isn't too big of a deal, especially with e-bikes (you can either use a cargo bike or a trailer and two seats).