Technically, yes, IMHO. Or at least, a statement like “That older person should be wearing less revealing clothing to hide their unattractive wrinkles and sags” is pretty body-shamey.
Compare that to an observation like “For a whole host of social and historical reasons, humans, unlike other primates, have developed a widespread cultural abhorrence of the natural physical changes that happen in aging bodies. It’s not merely that most humans don’t find old bodies as sexually appealing as young ones, but that humans are constantly taught that the appearance of old bodies is visually repulsive and even shameful, and should be concealed as much as possible. This entrenched shame and dread about aging has culturally normalized the idea that older people should be reluctant to reveal more of their bodies than absolutely necessary, and that older people dressed in fuller-coverage clothing appear more ‘appropriate’ and ‘look better’.”
That latter observation, although much longer-winded, is a more sensitive and thoughtful way to approach the issue than some prescriptive pronouncement along the lines of “older people need to cover their bodies more because their bodies are ugly”.
It feels very natural to us (at least once we’re beyond early childhood and have been sufficiently indoctrinated into cultural attitudes) to think that our revulsion towards gray hair and wrinkles and sags is merely instinctive, because they’re objectively ugly. But it’s no more natural or innate than the equally strong conviction among millions of people in 19th-century societies with color bars that dark skin was objectively ugly.
TL;DR: Gray hair, wrinkles and sags are not unhealthy or polluting or evil. Our aversion to seeing them is culturally learned.
Acknowledging that this cultural aversion exists and exerts a strong influence on our preconceptions about what older people “ought” to wear is not body-shaming.
Naively taking those cultural norms at face value and expecting older people to comply with them in order to “look better” often is body-shaming.