be taken with a pinch of salt	to be doubted / considered untrue
at death’s door	about to die
off colour	unwell
full of beans	very lively and energetic
go downhill	to get worse in health / quality / status etc
nothing but skin and bone	very thin
a shadow of my former self	weaker or less capable than one used to be
up and about	active after an illness
as strong as an ox	very strong and fit
ripe old age	very old age
kick the bucket	to die
alive and kicking	still alive and active
touch and go	uncertain
the writing is on the wall	a sign / warning of danger / unhappiness / failure etc
hold sb’s own	to manage despite
grin from ear to ear	to smile broadly
there’s life in the old dog yet	one is still physically / mentally energetic despite old age
as blind as a bat	blind or unable to see well
get one foot in the grave	to be near death
run out of steam	to lose the energy that one had previously