Help with understanding who I am. That it's ok for me to be useless at some things and I'm still a valuable person worth loving and respecting despite those areas where i lack skill. Therefore not having my self-esteem completely trashed by constantly being told that if I just tried a bit harder I could do everything everyone else can. I can't.
On the flip side, I outperform even very able NT people on various things which have enabled me to carve out a very successful career. Had I been diagnosed in childhood, felt secure, not having to mask and hide myself constantly for decades, I could have achieved far more with the energy that took from me. Productive things. Things that would have meant I pay even more tax into the system.
I could have had reassurance. People to teach me about budgeting, social relationships, self-care, recognising and naming feelings, controlling impulses, to foster self-worth. All kinds of things that I needed and did not get, not in a way I could access them. Like many undiagnosed autistic people.
I spent many of my formative years feeling very lonely and suicidal.
I would not have been so unhappy for much of my life if I had had a diagnosis, if that has any value to you. As a PP said - while extra support would have been good - the self-understanding that comes with diagnosis is the most important thing and oh my goodness, I can't imagine how I could have flown if I'd had that 30 years earlier. That is what I will be giving to my children.