Is being middle-aged really this bad? My parents are scaring me!?

My mom is 50 and my dad is 55. I feel like they are ALWAYS complaining about their age and how their bodies just aren't what they used to be. Even when they are not actually complaining, they constantly act like they are 70!

Both of them complain every single day of sore bones and muscles, my dad cannot get up out of a chair without grunting and cringing in pain and a lot of times he walks hunched over because his back is so sore, my mom is a kindergarten teacher and she can no longer sit on the floor with the kids during Sharing Time because she won't be able to get back up without help. Neither of them can see worth a crap without their reading glasses, my dad reads with a magnifying glass (along with his glasses) and my mom often needs her reading glasses, a magnifying glass AND a flashlight to read a book or the newspaper, they are CONSTANTLY asking me "what does this say? I can't read it..." You literally have to yell at them if you want to have any chance of them hearing you when you talk to them, the volume on the TV is always up so loud you can barely hear yourself think. I swear to God they need hearing aides but they refuse to admit that it's that bad, but trust me IT IS!! My mom has hot flashes at least 20 times a day and nearly freezes the rest of us out when she opens every single window in the house in the dead of winter time. They both take about 10 different pills and medication a day, their memories are TERRIBLE (if I tell them something today, there's only about a 30% chance they'll remember it by tomorrow), I am sooooo used to telling them the same thing countless times over because they forget from day to day, they need to take at least 1-2 naps a day or they can't function, they cannot stay up later than 10 or 11 at night (even on new years), they refuse to drive at night now because they say their eyes can't handle the lights of oncoming traffic, etc etc etc. The list goes on and on and on.

I understand that as we age, our bodies change and as is commonly said, "things just aren't what they used to be." I totally get that. That's just a fact of life. But really, are the changes your body goes through this drastic and this sudden? My parents weren't like this 5 years ago! And really it's only been in the last year or so that I've noticed these things getting A LOT worse. They seriously act like they are 75 year old senior citizens, when really they are only in their early to mid 50s! Is it like this for everyone? Because seriously, this scares me! Not only because I am not married yet nor have any children and I don't want my parents to be in senior homes and completely dependent on my sister and I before they become grandparents, but I don't want this to be my life when I get to be their age! I look at them and think "wow, this is what I have to look forward in only 30 years, what a nightmare!"

Is 50 REALLY the age when your life (or more so your body) starts to go down hill?