How could I use a switch statement for this lesson?

You won’t get any argument from me. The above is just a demo, not a recommendation.

To drive home my point about functions eclipsing everything else, this is all one big expression, not a single statement (other than the expression itself)

// entry point / main
(default_ => (switch_ => (life_cycle => (
  console.log(life_cycle(-1)),
  console.log(life_cycle(0)),
  console.log(life_cycle(3)),
  console.log(life_cycle(13)),
  console.log(life_cycle(20)),
  console.log(life_cycle(65)),
  console.log(life_cycle(75)))

// life_cycle
)(switch_(switch_,
  [ [age => age < 0 || age > 140, () => "This is not a valid age."]
  , [age => age < 3,  () => 'baby']
  , [age => age < 13, () => 'child']
  , [age => age < 20, () => 'teen']
  , [age => age < 65, () => 'adult']
  , [age => age < 75, () => 'senior']
  , [default_,        () => 'elderly']
  ]))

// switch_
)((switch_, cases) => (x, i=0) => (
  (([condition, result]) =>
    condition(x)
    && result()
    || switch_(switch_, cases)(x, i+1)
  )(cases[i]))

// default_
))(() => true)