Having limited availability and being a minor, and all of the scheduling restrictions that come with it, are probably why you didn’t get the job. Spot likes to have open availability. Basically, they want your availability completely open so they can schedule you whenever they need you, then they schedule you for one four hour shift a week, and often that shift is something undesirable like closing on Sunday night. Just saying.
Beyond availability, can’t speak for the ETLS, but as a TL I was looking for someone who was interested in the job, seemed motivated, appeared to be intelligent enough to handle the job and responsible enough to show up when scheduled, and, most importantly, someone who would be pleasant to work with and would fit in with the team, because I wasn’t just hiring a new TM for Spot, I was hiring a new member of my team, and it’s all about the team. Being dressed appropriately helps, and it’s a plus to say something nice about Target, but you don’t have to go overboard with it. Everyone is nervous answering the questions, those who are interviewing for their first job especially so, and I took that into consideration. There is no “right” answer to the questions, your answers just give us a clue about your experience, how you approach problem solving, how you think on your feet, and how you fit into a team.
The thing is, every interviewer is different, what would get a job offer from one might be a dealbreaker for another. Sometimes it isn’t you, it’s them. Don’t beat yourself up over not getting this job, your availability and age were likely the dealbreakers, and now that you have been through the interview process once, you will have that experience to draw in for your next interview, whether at Spot or elsewhere. Good luck!