I can imagine a future generation where gender fluidity becomes
   a side-effect of human life expansion [physicists make
   everything spheres, so a genderless human would be a logical
   result].

   and at around the age of 4 years old, children are asked by
   their caretakers to chose their gender. Little 9xj2.997a.alpha
   picks up the annoyed Thomas the Train and points it at
   caretakers face.
   [1]no
   "But honey, school is starting soon. You have to choose."

   9xj2.997a.alpha picks up toy train again.

   etc.

References

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   1. http://icopiedyou.com/wp-content/uploads/2015/08/no.jpg