I do not negate or confirm whether he has created a new universe or just come to terms with his pubescent angst... I would say it is just as likely that he is merely coming to terms with death? But, what is the difference? That is the beauty of the story. It could be all three... I mean, creating a new universe and now becoming its god, that's insane. Not to say impossible, but in our view it would be the same as death.
I am curious about the puberty undertones, I can see that but I have to say undertone, no more. I feel that Akira is social commentary at it's peak and puberty may be a theme, but not the main one. I like the idea of a new universe but I feel that it is not obviously stated. Yet I cannot deny that it is a great analysis of the ending. So, having never read the manga, because I am a cheap jerk or whatever, I feel that Tetsuo dies. He dies, only in our eyes. It is a perfect ending. We do not know what comes after death, and I agree the theme is about the Star Child, human evolution, 2001 Space Odyssey, etc. So all these interpretations are essentially the same ending. AMAZING. I don't know. AKIRA! Every time I watch it I am blown away. Tears. Amazed. Or as Kei said, "Fantastic."