Seeking adult diagnosis = Hell (rant/vent post)

I'm frustrated when I type this and yes this is a venting post because I'm overwhelmed by the situation.

Why is that there is everything out there all readily available for children young adults when it come to diagnostics and services for assessments but once you get over the age of 25 everything just dries up? Like I get that they are the people who need help with like schools, college and uni but what about the rest of us? Okay yes I should have taken it seriously at 17 when I was told to get my ADHD reassessed but just in general I don't get why all the resources go drier than ghandi's flipflop just because I'm of a particular age (I'm almost 31 for context).

The resources on here for assessments and Right To Choose are great and everything it's a nice catalogue which I'm more than sure does help but everything on there that would be suitable for what I'm looking for has a cut-off age of 19 or 25 and I'm sick to the back teeth of arguing with my doctor's who only seem interested in my anxiety and depression and their dismissal of everything I tell them I am experiencing. Seeking an adult diagnosis or even just the assessment is feels like literal hell.