animal.rb

class Animal
  attr_accessor :name, :age, :weight

  def initialize(name, weight, age)
    @name   = name
    @weight = weight
    @age    = age
  end

  def to_s
    "I'm #{name}, I have #{age} years and I weigh #{weight} KG."
  end

  def older?(animal)
    age > animal.age
  end

  def bigger?(animal)
    weight > animal.weight
  end

  protected :age
  private :weight
end