"OLD" lady with a beer after biking 36+ miles over 10 PDX bridges!
They can get fat – but so can a 3 year old! Do they have to get fat? Of course not. Metabolisms change but the changing of one's eating habits and the increasing of exercise will do wonders about weight.
[I'll let you in on a secret - this works for all ages!]
I hear people say this and I am not sure what they mean by fragile. Do they think bones just break, that older people fall all the time or are so weak they can't move around?
Bones lose density; especially for post-menopausal women but there are ways to help that not happen. Now that we know more about osteoporosis I expect we will see fewer older persons who develop the hunched over position.
As for fragility? Ski areas on Mt. Hood in Oregon offer free skiing for those over 71 or 72 depending on the area. I've met skiers over 80 skiing away there. Fragile? Nope. Maybe the regular skiing keeps them strong?
I teach lifespan human development and many in my classes are nurses. A student once said that he never realized that older people could be healthy – his entire experience with persons over 65 was in a hospital. It was an "AHA" moment for him to learn that he [and we] know little about healthy persons as they age – precisely because they are not in hospitals or assisted living homes where studies can easily be done.