There's a possibility that they don't die, even if the age bar is full, that's not a bug.
As for the age not showing, did it ever show of any of your Sims that reach the end of their live ? IIRC, that's been the case for along time now. I once played on long and my Sim lived to be over a 1000 Sim days old but I had to use MCCC to find out how many days she had lived. I'm unsure though if it's always been the case.
I went to take a look at the age of my sims and I can't see there age at all whether there young are old
as far as how long elders are suppose to live after an age bar is full I don't know I know its suppose to be different for each one though I like the surprise of not knowing when they will die
