A intenção era só simplificar e ganhar todos os métodos sem precisar fazer muito, é muito simples fazer em uma classe desprendida do ActiveRecord

searching.rb

module Searchable
  included do
    scope :gender, ->(gender) { where(:gender => gender) }
    scope :birth_on, ->(date) { where(:birthdate =>date) }
    scope :birth_before_than, ->(date) { where("#{quoted_table_name}.birthdate < ?", date) }
    scope :birth_after_than, ->(date) { where("#{quoted_table_name}.birthdate > ?", date) }
    scope :profile, ->(profile){ where(:profile => profile) }
  end

  module ClassMethods
    def fiter_with(options = {})
       relation = all
       options.each do |key, value| 
         relation = relation.send(key, value) if available_scope?(key)
       end
       relation
    end

    def available_scope?(scope)
      %w(gender birth_on birth_before_than birth_after_than profile).include?(scope)
    end
  end
end


# Exemplo:
# search = MySearch.new(User)
# search.filter_with(options)
class MySearch
  attr_accessor :klass

  def initialize klass
    @klass = klass
    add_scopes(@klass)
  end

  def add_scopes(klass)
    @klass.class_eval do
      scope :gender, ->(gender) { where(:gender => gender) }
      scope :birth_on, ->(date) { where(:birthdate =>date) }
      scope :birth_before_than, ->(date) { where("#{quoted_table_name}.birthdate < ?", date) }
      scope :birth_after_than, ->(date) { where("#{quoted_table_name}.birthdate > ?", date) }
      scope :profile, ->(profile){ where(:profile => profile) }
    end
  end

  def fiter_with(options = {})
    relation = @klass.all
      options.each do |key, value| 
        relation = relation.send(key, value) if available_scope?(key)
      end
    relation
  end

  private 

  def available_scope?(scope)
    %w(gender birth_on birth_before_than birth_after_than profile).include?(scope)
  end

end