As long as you are a service member in good standing or a spouse of a service member in good standing, then you are eligible to take the exam. Furthermore, you are allowed to take the exam as many times as you want as long as it hasn’t been less then six months since the last time you took it.
There is information on the web that states that you cannot take the DLAB again if you receive a passing grade, however this is false and not true.
Therefore, the only thing stopping you, a good standing service member, from taking the DLAB is yourself. So remember to test early and test often.