Once you are over 18, you are not too young to plan.  An estate plan is more than where do your assets pass when you die.  Estate planning is also about designating agents that can pay bills or make medical decisions on your behalf should you become incapacitated.  It is also important to ensure that assets that you may have acquired prior to your marriage have the proper titling or beneficiary designations so they do not need to be probated should you or your spouse die.