Is it too late for me to get diagnosed?

Hi everyone! I'm 23 years old, and think I'm experiencing significant ADHD symptoms that interfere with my daily life. It was suspected by a teacher in second grade since I was struggling so much, but my mom was averse to the idea and insisted I was gifted and needed to be put in harder courses. This eventually burnt me out by high school, and I began regularly skipping, failing courses, and nearly didn't graduate.

Fast forward to university, and I had to drop out because everything felt so difficult to the point school felt like drowning. I've had numerous other difficulties in adult life with remembering appointments, general organization and cleaning, etc. I feel lazy and awful and broken.

I've been in intense psychiatric treatment for 3 months, and things are starting to finally look up for me and I want to go to school again. However even with a higher mood all the struggles with focus, organization, etc are present. I can barely keep a clean house let alone study. I think I need to get assessed but I am nervous both because I am worried they will see me as drug-seeking because of my SUD diagnosis, as well as being worried that it is "too late" for me, since every ADHDer I know in my life got diagnosed either in childhood or around 18-20. Does anyone have experience with later diagnosis/pursuing ADHD diagnosis as someone with a SUD diagnosis?

Thanks!