Variable de instancia: self vs @

Aquí hay un código: 

class Person
  def initialize(age)
    @age = age
  end

  def age
    @age
  end

  def age_difference_with(other_person)
    (self.age - other_person.age).abs
  end

  protected :age
end

Lo que quiero saber es la diferencia entre usar @age y self.age en el método age_difference_with.


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