They shall still bring forth fruit
nuwb (noob)
to germinate, i.e. (figuratively) to (causatively, make) flourish; also (of words), to utter -- bring forth (fruit), make cheerful, increase.
in old age
seybah (say-baw')
old age -- (be) gray (grey hoar,-y) hairs (head,-ed), old age.
they shall be fat
dashen (daw-shane')
fat; figuratively, rich, fertile -- fat.
and flourishing
ra`anan (rah-an-awn')
verdant; by analogy, new; figuratively, prosperous -- green, flourishing.