If your US passport has expired, then it would be wise to renew it as soon as possible. The unpredictability of life suggests that these things should not be left for the last moment as you never know when you would need to travel internationally.

If your previous U.S. passport is less than 15 years old, and you were above 16 years of age at the time you obtained it, or your current passport is not damaged and you still bear the same name, you are eligible to apply for it by mail. However, if you fail to meet these criteria, you will have to apply for it in person. In any other case, you can do so by mail. If the passport has to be renewed via mail then a completed, dated and signed