Fit Old People

Has anyone ever been around healthy old people? I mean people over 70 who are still active, healthy, and mentally present. Have you noticed anything about them? I attended my FIL's 70th birthday party and almost everyone who was there was between 70-80 years old. These folks were dancing to Motown, doing lip sync battles, and doing every line dance possible. Now I will be honest, they all did leave around 9:30 to head home and go to bed, but they really partied while they were there. The thing that I noticed about them was that they were all thin and had good control over their weight. Not that obese people weren't invited (afterall, I was invited), but most of the obese guests were either sickly, on walkers, or in wheel chairs and couldn't attend. I am not making any judgements here, thin people get sick and have health issues all of the time. This is simply an observation of what I saw at this party of over 150 elderly attendees. No scientific study could have been more influential than actually seeing these lively, fun elderly folks get their "party on". It seems to me that if you want to have quality of life late into 70's, 80's, being at a healthy weight increases your chances of being able to do so. What do you think about my observation.