Of course everyone is different, some people need more sleep than others. I get the sleep I need, otherwise my body clock would tell me I needed more.
And I would think if 80 year olds were eating junk food, their health would be bad. You can get away with eating crap when you are young, by the time you reach 80 (if you were still here) you most certainly would know about it.
My mom had a pretty shitty diet. She was blessed with good genes. Her mom lived to 96. My mom was pretty spry at 80. Definitely not overweight.
But it did catch up with her, and when it did, it debilitated her pretty quickly and likely killed her years earlier than she should have gone.
Good genes are a blessing, the rest is down to lifestyle and luck.
My mum was 93, my MIL was 104, so hopefully me and OH have iinherited those good genes too.