What tests would you write for these two simple Ruby objects

Imagine you wrote this simple PORO in your Ruby on Rails app:

class CreditCard::AgeValidator
  def initialize(age)
    @age = age
  end
  
  def valid?
    return true if @age >= 18 
    
    false
  end
end

What tests would you write for it? 

What cases would you cover with your tests? How many tests would you write?

What about this update_required? method. 

What cases would you cover when testing Account#update_required? 

What cases would you cover with your tests? How many tests would you write?

class Account < ApplicationRecord
  \# t.date "expires_at"
  \# t.string "website"
  
  def update_required?
    website.blank? || expired?
  end
  
  def eternal? = expires_at.nil?
  
  def expired?
    return false if eternal?

    expires_at < Date.current
  end
end