First off, congrats on graduating early and on your publication! You sound really cool. I also applied right out of undergrad and didn’t get in. I heard from professors that people almost NEVER get in right away because the programs like to see that you can write on your own without needing school deadlines and prompts. in general, mfas have a lot of free time to write and it is really up to you to motivate yourself. They also know people who are afraid to graduate might just want to use a masters as a safety bubble before having to work full time. Either way, if they find someone who is really good but is a senior in college, they might just decline them because they figure they will be even better in a year and will be more emotionally ready.
There is a blog called the mfayears where people talk about their experiences. This one guy talks about graduating early and then going to Iowa. It can be really hard for some people to adjust when everyone is older or they just see it as another year or so of school. Older applicants with kids and such seem to really appreciate the time they get through the program and use it to their advantage the most.
There are also some really great interviews online for uiowa on tips for your application and questions about age. I would look at those.
good luck! It could definitely happen! But know that as a rule most programs prefer to see people after they have been working so that they know they can motivate themselves to write independently. https://youtu.be/fP91bdaJ-G0
https://youtu.be/rI0M3zbdRvM
www.readtheworkshop.com