How do you get over the fear of getting old?

I'm going to be in my 30's soon and it's scaring the shit out of me. I'm worrying about lower testosterone, getting uglier and not being able to get women as easily (due to things like balding and graying), having health problems, erectile dysfunction, losing energy and not being able to lift or work out as much, etc. I also can't stop reflecting about the past and thinking about the events in my life. Also thinking about some of the stupid decisions and some of the years I wasted when I was younger and ruminating constantly.

I keep seeing these lame people in their 30's to middle aged years and that were previously in good shape, cool, stylish, and now they're lame as fuck. Does this come naturally with age, or were they just lazy fucks that let themselves go?

OTOH, I know a guy that's in his 40's and he's somehow banging hotties half his age, is ultra stylish, in great shape, owns his own shit/housing, etc.. Why don't more people end up like this?

It feels like I'm having a midlife crisis extremely early.