How can I stop mental obsession with growing up/time/aging?

God I got this annoying "mental disease," its agonizing, very painful, painful just writing it here. I am soooo scared to grow up. And all throughout the day I have these thoughts that continually circle around about how sad it is that everyone is growing up (including me) and yes just thoughts about time/aging/growingup. How can I get my brain to stop thinking about it so much? ITS SO ANNOYING and it DEPRESSES ME SHITLESS.