None of what you mentioned would automatically disqualify you with any police departments that I know of. But, it could make it difficult for you to get hired. If there are plenty of other applicants similar to you that haven't been fired from jobs, you probably won't get hired. If you were fired once or even twice, it wouldn't look so bad. Nineteen is still relatively young though so it shouldn't hold you back forever if you're an otherwise good candidate. If you've had a job since then, hopefully you'll get a good recommendation from your supervisor. If you haven't had a job, you should get one, and start improving your work reputation as soon as possible. Maybe even consider getting a full-time and part-time job or two part-time jobs. Let us know how it goes.