It is likely you are on a catalog that does not align with the minor. The MS&E minor is offered on the 2018-2020 and future catalogs, so you will need to inquire with your academic advisor and see if switching catalogs is an option for you.
Generally, you can still apply for the minor in this case. We are primarily looking to see that you have at least 4 semesters left in residence at UT Austin. If you do, we will likely accept your application, assuming you meet the other requirements. As always, if you have specific questions about your situation, contact the minor coordinator or advisor.