Identifying properties of is_prunable?

prunable.rb

class Prunable
  THIRTY_DAYS_AGO_SEC = 60 * 60 * 24 * 30

  def self.from_assets(exclusion_time, assets)
    assets.select do |asset|
      self.is_prunable?(exclusion_time, asset)
    end
  end

  def self.is_prunable?(exclusion_time, asset)
    sec_ago = 60 * 60 * 24 * 30 # 30 days
    asset.created_at < exclusion_time - sec_ago
  end
end