Baltimore Co., Maryland They require subs to be at least 18 years old and have a high school diploma. It has worked out great for me. However, some subs that work in the schools are horrible (those with and without degrees). In my (biased) opinion, it's all about why you are there and not how old you are. Experienced subs are few and far between (as it is either ed. majors, career changers, or mothers that want to be home when their kids get out of school). The subs that have subbed for years usually don't have an education; just their experience (which can be good or bad depending on their experiences).