Odds of Hanging On
If you want to hang on to this career, most stores will be more than happy to oblige. It costs them money to train new employees—more than $3,000 (source).
However, people don't often stay for long. One-third of grocery store employees are between the ages of sixteen and twenty-four (source). Even with the manager title, working at a grocery store isn't often considered a lucrative career track.
If you look at the job and think the work is satisfying enough and the particulars (hours, effort, responsibilities, etc.) are at the right levels for you, you should be able to hang around as long as you'd like.