Enrollment medicals aren't good for 5 years prior to actual enrollment. In fact, up until recently, they were only good for a year after enrollment, regardless of how old you were. To keep your file open, IIRC, you have to do at least a questionnaire once a year and note if there are any changes in your condition or history (new diseases, owees, surgeries, etc). This of course, changes with the wind.
MM