Stomach can be awfully bad with old people (7)
I believe the answer is:
abdomen
'stomach' is the definition.
(synonyms)
'awfully bad with old people' is the wordplay.
'awfully' indicates an anagram.
'with' says to put letters next to each other.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'people' becomes 'men' (men are people).
'bad' with letters rearranged gives 'abd'.
'abd'+'o'+'men'='ABDOMEN'
'can be' acts as a link.
(Other definitions for abdomen that I've seen before include "Region of the body between the thorax and pelvis" , "gut" , "pot" , "Where one digests" , "Site of corporation" .)