* Aggies (with a capital A): This is a common nickname for students and alumni of Texas A&M University.
* aggies (with a lowercase a): This could refer to a group of people who farm or work with agriculture, or it could be a slang term for someone who is considered slow or unintelligent.
To be sure of the correct spelling, you need more context. What is the sentence or situation in which you are using the word?