I don't know of any cheat, but if you're not opposed to mods, MCCC allows you to change their ages without going into CAS. You can also target a Sim to have them die, if you wish. (I have only used this twice, but that's because I was playing my ancestral game save, and my sixth great-grandmother's dad died in 1770, and my sixth great-grandfather's mother died in 1773 before the family left Virginia. To this day we don't know exactly when Joannah left this realm, or the cause of her decease. The only trace we have of her is the very last time she signed on her husband's behalf on a land-transfer deed, which was 15 Aug 1773. The family left Virginia in early December 1773. Even some historians are unsure if she went with them. So, I had to decide which death and then I just clicked on her and she was no more. :O
