Speaking as someone who only got our ADHD diagnosis in our late thirties and our autism spectrum diagnosis at forty fucking two, please consider just telling them. That could be years or decades of social, pharmacological, and even legal assistance that they deserve and need and aren't otherwise getting.

I agree with this.

My ever optimistic self would fail and fail and fail, create a system, fail, create another system, fail, .... at seemingly easy things.

As soon as I had a rational reason for otherwise inexplicable challenges, enormous amounts of stress evaporated.

Now I know what things are a lost cause: So I get help, delegate, find another way. Being bad at something, and recognizing it, is not the same as failing.

Second this too. I went through live until mid thirties thinking life just was that hard for everyone and I was just bad and shit at things, worse than others - I suffered alone thinking everyone had to be like me, because I'm normal right? It was a huge relief finally being diagnosed because I could finally understand myself better, even found community of sorts.. strategies that worked for others and most of all.. just allowing myself to be KIND to myself, not always beating myself up, being angry at myself for being shit.

Resonate and agree with this 100%.

Also agree with this, but want to caution: Bring this up as gently as you can

Don't accuse them of being ADHD, or insist too strongly

If you do bring it up, I would say make sure to really emphasize that you don't think they need fixing. It's something that might help them overcome their own struggles, not something to make them a better person for others, you know?