so his death certificate and gravestone must be incorrect - maybe his son (who registered the death and perhaps commissioned the gravestone) knew his birthday but not his age or birth-date!
Perhaps. Why not check the births register. There's no doubt what last February or February last means, however I'd bet money that the newspaper did NOT report:
"At Cape Town, Cape of Good Hood
, on the 2d
February last, the Lady of Dr John Forrest"