To be honest, the re-enlistment stats will always be low. If your 17 > 25 when you join up, your young and fit. Few people aged 30+ really want to rejoin the armed services, they have cumulative injures and a greater risk of physical harm from the training regimes. That and they would rejoin at the level they left, minus the lag time for the years out of service, they end up in a disadvantaged position both physically and financially. That and the fact they left the military service for a reason, like you leave any job, and are not likely to change their minds.
What's more interesting is the percentage of people who remain in military service all there working lives, compared to any other job. The re-enlistment stats are a moot point.