Kaetemi
An aged character can be healed, but won't be able to respawn, so the permadeath would kick in when the death timer runs out.
Imagine the very high, very un-fun stress experienced by a healer running as fast as they can to reach a comatose aged character and arriving with just one or two seconds left on the timer--seconds wasted by an interrupted spell. Poof. Angst ensues all around.
Might work better if the respawn timer was longer for an aged character. Somewhere between six and ten minutes (not suggesting a variable time, just not sure what the best amount of time would be).
On the other hand, this point can be said to circle back to this other point:
Kaetemi
Your elders will need protection then.
What would be the lore behind this, though? As a homin ages, the "nanoseed" that allows them to respawn wears out? In that case a chance of permadeath might make more sense (there would/could/should be a very clear distinction between a normal respawn countdown and a permadeath countdown).