Elderly and small hand people find it easier to use a smaller dishcloth. My elderly 90 yr old Mother preferred 6 1/2″ to 7 1/2″ instead of full size dishcloths. Using a lighter material is also helpful for elderly to handle.
The actual size of a knitted piece can be affected by yarn weight, needles used, pattern size selected, and knitting style tension. Each knitter has their own actual style and tension even if they are using the same technique of knitting. You should use the same tension throughout the piece. I have to make sure my tension is the same at the sides [edging] and borders [top/bottom or caston/bindoff]. Many knitters use a different cast on or bind off needle size than they use on the whole piece.