I'm pretty sure the reality is exactly the opposite of that. Healthier lifestyles increase the amount of "later life care." See Japan as a perfect example, a very healthy aging population creating massive care market (and a big burden on the infrastructure).
People who live a healthier lifestyle live longer, and then get sick from old age (unavoidable). Which increases the amount and length of care. People who live an unhealthy lifestyle never make it to 65, thus never need "later life care" at all.
> For example, if we promote healthier eating habits, we might reduce the amount of late life treatment needed for obesity, heart disease, and diabetes.
Most people with those types of conditions (due to lifestyle, not age) never make it to Medicare. You still get the age related versions of those, and you get things like hip/knee replacements, broken bones, cocktails of daily drugs, cancers, strokes, and so on.
No amount of healthy lifestyle will make older people cheap to care for. All you'll do is increase the pool of older people by promoting healthier lifestyles.
If your goal is to increase the max average age of your population then healthier lifestyle promotion is going to accomplish that. If your goal is to reduce cost then doing "nothing" (and literally letting people die from their own neglect) is the thing to do.
People who argue the whole "fatties/smokers cost us money" thing haven't even given it a tiny amount of thought. Both groups die young, older people are the most expensive care period, therefore fatties and smokers never make it to the super-expensive part of their lives which is "good" (in financial terms, not moral terms).
Do those groups get sick at younger ages? Yes. But propping someone up with diabetes from 40-50 is nothing in cost compared to keeping someone healthy from age 65-75, because at 65-75 you'll still likely be treating diabetes but on top of that also tons of other ailments introduced by age.