First of all, forget about the age thing and take your time with this decision.
If you have a diagnosis from a professional that has fairly recent documentation, you can probably get some extra time on the GRE. Look into that.
Do you any experience with “professional writing”? Many internships, including many at non-profits in cultural or service areas, need interns who can write. There are also jobs to be had, that require good writing. I wonder if you would consider doing an unpaid or paid internship first, whether in the publishing industry or elsewhere.
If you really want to do a master’s, I can understand why you would want to continue where you are, since it’s comfy, doesn’t require a GRE, and you may know faculty. And it may be convenient in terms of location and continuing your life. If WP works for you, don’t let anyone dissuade you.
I think it is important, even at the grad level, to make sure the education you are getting is worthwhile, rather than focusing only on employability. Amy grad school, if it funds you, offers a sort of laboratory for development, and that can be valuable regardless of outcome. If that is available at WP, that’s fine.
I know there are some online and low-residency writing programs as well. Look at Goddard, and Lesley.
Now, about the ADHD. I have a daughter in her 20’s with ADHD and completely understand. You have done magnificently. Don’t know if you use medication or meditation or what your strategies are. Clearly it is good to keep the number of classes down. Leave time for yourself so don’t work full-time if possible. Register with the disabilities office even for grad work. You may find things more flexible than undergrad, depends.
My daughter recently tried lessening work and increasing classes and it didn’t work out. She lost some money- this once- the cost of one class. I think it was good information. She now knows how much work plus school she can handle. You may need to experiment a bit.
I will tell you that in both paid and unpaid work I have done a lot of writing and never finished college at all. I sometimes started kind of low in an organization and worked myself up, sometimes quickly. I often wrote newsletters, brochures, donor letters and info sheets. In a varied job, this kind of thing was challenging and fun. So consider the various ways in which writing can be used at work: every company and organization needs writers.
You can also work as a tutor or coach.
Finally, why publishing?