...manly chest is replaced by a spare tire at a somewhat lower level..

I remember my Dad, 75 yrs old and a Cockney, having a little rhyme for this process....

When a person to the age of 40 doth come,
for a man it goes to his waist.
To a woman, her bum.


or words to that effect. I'd be interested if anybody has heard the correct quote and/or can attribute it.

stales