Aging's a Bitch

I have had a lot of friends freak out about turning 30. That was never the case for me. Sure my skin was dewier at age 20 and I had a bit more energy and pep, but 30 never bugged me. Hell, I'm not that far from 40, and that part doesn't bug me. Much.
Except now I am starting to have a few little gasps of anxiety. Not so much about that number, but the ones beyond. One good thing about these days is you're no longer really old when you're 50, since we have celebrities like Demi Moore and Madonna looking pretty damn good for their ages (though Madonna's arms still scare me.) Even older women, like Meryl Streep or Martha Stewart, look pretty good. Period.
But two things do scare me.
One, I don't feel my age. I feel wiser and more confident than I did at 20, but I don't feel like I'm nearing 40. I would say I feel at least 10 years younger. A good thing. But sometimes I wonder if I'm maturing right. Does that make sense? I feel 25. But I probably should not be acting that way. Of course, at 25, I would sometimes be up all night drinking or partying, thanks to a night shift and impressive tolerance for beer. Now, I don't feel the need or the desire to imbibe so much, or barely at all, and that's not a bad habit to acquire.
Plus the rules of aging are changing. My father-in-law is somewhere around 80. I never quite remember because he doesn't seem like he's that old. He comes across as much younger. One, men age better than women, and two, he's got an active and lively mind. Same goes for my mother-in-law. She's several years younger than her husband, but she doesn't come across as "old" either.
But by comparison, my mother is very close to my mother-in-law's age, and she is coming across as old. Really old. Bad old.
She is what scares me the most about aging. She had a mild stroke nearly a decade ago, and she is getting into probably a mid-stage of dementia. She forgets, she gets confused, she can't focus, she's paranoid, she remembers things that never happened. And she's weak. She can only walk a few steps and then she's winded. (She still smokes, probably two to three packs a day, by my estimate.) She has arthritis, back troubles, sore spots, aches, pains, weakness, walks hunched over, and on and on. She definitely is the villain, or her condition is, in the horror story of aging.
As I read up on Alzheimer's and dementia, it makes me scared of what the future may hold. And it makes me want to avoid that. I hope to see the light and take better care of myself. Exercise more. Eat healthier. Keep an active and lively mind. Socialize. Nothing is a guarantee against dementia or Alzheimer's, but there are steps to take to try and fight it off. I can take losing elasticity in my neck and face, but to lose the firmness of my mind, that scares the hell out of me.