I was promoted pretty young and looking back the transition went pretty good, but there were a few things I could have done differently. Firstly, don't back down when being challenged by someone who's older or challenges your authority simply because of your age. For example, when becoming GSA/GSTL, I had an older cashier who kept telling me that she was old enough to be my mother, and that she didn't understand why they promoted me so young (yeah she was pretty rude, in that sweet old lady kinda way). Over time, whenever I asked her to do something, she constantly sought to override me with another leader at the front and encouraged the other cashiers to not listen to me cause I didn't know what I was talking about. So I brought her in the office with another TL present and just had a conversation to clear the air. Turns out it was less an issue of how I ran the front and more of a fact that she had been dealing with personal stuff and just kinda taking it out on me. I told her that if she does have concerns to feel free to bring it up to me because I am straightforward and would rather just talk about it. It was a good learning experience for me also to just be able to listen to a TM without feeling like I needed to constantly talk or control the conversation and it did teach me to learn how to cater my message differently depending on the TM. Not all TMs respond in the same way to instructions, direction, and encouragement.
Secondly, don't be afraid to admit when you don't know something. This may be less of an issue with you at your store but sometimes with being promoted younger people automatically assume that you are a "know-it-all". I had to learn that instead of trying to make shit up as I went along, I got comfortable saying "you know, I am not at all sure what's best practice in this situation, but let me find out and get right back to you." I think it makes yourself more relate-able as a new leader in general. Lastly, find the balance between being professional and not taking yourself too seriously. One thing I did unconsciously was try to take myself too seriously and go over the top to show how mature I was, to the point where some of the team were telling me to loosen up a bit. You obviously don't want to go too far in the other direction where you're too much of a goof and not professional at all where your team will lack respect for you because of it. I ended up finding a good balance with my team of taking opportunities to share in valid frustrations, talk about their personal stuff with them at times, but at others let them know when we have to be able to buckle down and get things accomplished.
Sorry this ended up being a bit long winded but hopefully it helps you out somehow. Seeing as you've already been in the store for one year, your team knows your character, but it does get easier when you've been a leader longer than you have a TM. When I tell my new team members now that I started out as a cashier at 16 they just can't see it lol.