weak or delicate
frail - weak
A person described as being ‘frail’ is not physically strong or healthy, typically due to old age or a slightness of constitution or body structure. The term is also used to refer to a weakness in character or morals.
I went to the nursing home to see my grandfather yesterday. He was looking very frail.
Gary is young, but because he’s quite frail he tends to pick up a lot of colds and infections.
The famous actor's drug addiction led to his fall from grace. It was a classic example of human frailty.