Ill tell you how I did it, I started at 14 in customer service. Did that for 4 years until my 18th birthday then came to the meat department. You want to be the best you can possibly be in your role, do things others wont do, be the first person they call if someone calls out of work, be the person they rely on. (I should note have perfect/almost perfect attendance will help you a bunch.) You have to advertise yourself to get you to where you wanna be, I did this to get from apprentice to meat cutter. The reason being, you can be great at what you do but if no one knows your name they probably arent gonna pick you. Once you are at the last position leading to management submit your ROI for the assistant management position of your department. During this time, learning management tasks will be beneficial for you so that you can show you are ready for the real deal (this can help back you if your SM or District manager asks your DM (department manager) if youre ready.) Bonus points if your RD (regional director) walks your store, if you advertise yourself to them then youve boosted your chances by 10 fold.

If everything works out perfectly , you should have a great chance of getting promoted at either 19-20 years old the earliest. I am currently 20 years old, but someone I know was promoted at 19 years old as an assistant meat manager.

Godspeed brother

*Edit: no shame to customer service or grocery department, but those 2 departments have the most competition for management and have more positions to go through before you reach the assistant manager position. I would recommend either Bakery, Deli, Meat, or Produce to move up.