I mean, I am 30 and I don't feel like an adult at all.
I (my current physical body) will also be 30 on 2022.09.17.
Or am I doom to be the adhd adult who has a young mind forever?
This is not really a doom. This is a good thing.
Or maybe its a good thing my mind is young?
Yes. It is. And I write this as someone, who take almost everything too seriously. So I am your opposite. I was very serious even as a very young child. This is also good. Everyone is different.
I dont think its a good thing all the time though
Sometimes it is indeed good to approach things differently. I am not serious all the time either.