If your ultimate aim is to be a police officer, there are ways to plan for this by entering the military right out of high school. First, examine all of the armed services (talk to recruiters and read up on military service web sites). Do join the Marines if that branch of service holds a special place for you in your mind (you want the challenge of tough discipline, your family members served in the Marines, etc.). But given your final objective, it may be wise to seek out the service that guarantees you military police (security police, etc.) training and offers the best chance to do police type work. After all, you will be graduating from high school several years before you are eligible to be a civilian police officer, but you may be able to do that work in the military for several years before age 21.
You may want to check with the Peabody Police Department to inquire about their entrance requirements, including education. Many municipal departments (especially the smaller ones) will accept a high school education as an entrance requirement, but may require a college degree (associates or bachelors degree) for promotion. However, having college credits should help in landing a job. Also, you may be able to complete a two year degree or perhaps even a four year degree while on active duty in the military. If you have done well in high school, you might be able to pass a number of "CLEP" (College Level Examination Program) examinations where each examination passed will get you three semester hours of college entry level courses. Also, there are many legitimate colleges offering online courses to military members, which are often paid for by the military through tuition assistance (and your GI Bill is left intact). However, be cautious of the college you sign up for and be sure it is legitimate and respected. Take a look at such schools as Thomas Edison State College in Trenton, NJ, which has a good reputation for military and "distance" education.
The military will also provide discipline and experience, and will make you more competitive among other police department applicants. Just do not get in trouble in whatever service you choose, as that will ruin your chances for a law enforcement career. Also, Peabody has a relatively small police department (just over 80 officers total), so advancement may be limited and hiring cycles may be few and far between. Also, the strict budgetary constraints that are a product of our present economic hard times are actually seeing the reduction in size of many police departments. So you may want to look at surrounding police departments to see who may be recruiting. Also, just getting out of the military (and supposedly in good physical shape), you might want to consider the Massachusetts State Police, which has a very tough academy and a very good reputation and some excellent pay and benefits.
Best wishes, Z. G. S. Bear in Divide, Colorado