well in elderly you generally lose adipose/subcutaneous tissue (fat) in their arms/legs whereas around their trunk it may increase...depends on their lifestyle, are they walking or are they in a wheelchair all day/use lifts to get transported?
i would assume that the calculation may not be a proper way to measure body fat percentage. i'm in nursing and i've never seen them whip out a caliper at a long term care facility, they use BMI for a more accurate reading. so probably i'd say the biggest reason would be the accuracy of the results.
i'd also like to point out that nowadays we're taking extra care towards the elderly because pressure ulcers are becoming more common. they start when adipose/fat tissue becomes separated from the muscle due to shearing/pinching/pressure. we do as much as we can to avoid these because once oxygenation to the tissues become disrupted, cells start dying. i've had to clean, pack and dress a stage X ulcer before and it's not something i would want anybody to suffer.
as for young children, i would guess maybe because they are growing rapidly it wouldn't be very accurate either? babies - small children have baby fat or in medical terms, brown adipose tissue. they need this because they don't have shivering reflexes/ability to generate heat with muscle activity like adults do. | 