You are going to doubt yourself massively before, during, and after getting diagnosed. You most certainly are an ADHD person – this is part of the process.
Learn to accept what is there, rather than fighting against it.
Get ready to cut toxic people from your life.
I spent six years working against my diagnosis – trying to 'cure' myself.
Once I accepted it, I realised how many people had been exploiting boundaries, and being derogatory toward me for being ADHD.
I tried to educate them, if they continued, I removed them from my life.
You deserve people who love you for who you are, not what they want you to be.
Those people do exist, and it's healthy to let those go who make you feel negative constantly by harassing you over pretty insignificant stuff in the scheme of things.
You will also likely experience a mix of anger and depression for a while – these are healthy to have – they are not pleasant – but you need to grieve for the fact that it wasn't detected earlier. I had to work toward not getting stuck here as it was detrimental.
Find a community somewhere. It doesn't have to be Twitter, but you need somewhere that people understand the challenges you have – or how hard your life has been. The shame I experienced for a while after was due to not seeing people being open about struggling.
No matter how late in life you discover it, with the right introspection and reassessment of your life through an ADHD lens – you can develop a lot more self-compassion, and go on to enjoy your life once this is done.
Most importantly ADHD traits are not a moral failing.
Once you get past seeing yourself as broken or if you never think that and you still feel stuck – if you can get a coach. I became one because it was the only ‘therapeutic’ support that worked.
It helped to have someone who helped me cultivate trust in myself again.