I understand that you're scared of getting old... but it doesn't HAVE to be a bad thing. I think with age we realise what's important in life. I think often times it's the later years in life that we REALLY enjoy ourselves and find peace.
Oh and who says your beauty is going? Who says only 18 year olds are beautiful? What isn't beautiful about a woman of 80 or even 100? Beauty is in who we are as people, and that is something you take with you through the whole of your life. I think with age we become wiser, we learn what and who is important in life... I think that is something to look forward to.
I do understand that you're struggling with this anxiety and I have read your reasons too, and they're valid... but you're spending so much time worrying about the future, are you really making the most of the present? There's so much fun to be had

(sorry I must sound annoyingly positive here lol I'm having a good day).
I'm gonna look for an email fwd I recieved once, it always cheers me up about aging.