human.rb

require 'date'
class Human
  attr_reader :name
  attr_reader :dob

  def initialize
    @dob = Date.new
  end

  def christen(name)
    @name = name
  end

  def change_name(name)
    @name = name
  end

  def age
    Date.new - @dob
  end

  def adult?
    age > 18
  end
  
  def older_than?(other)
    age > other.age
  end

end

bob = Human.new
bob.christen('Bob')
bob.adult?
# => false

alice = Human.new

bob.older_than? alice
# => true