The latter is really not an issue, as we all know that looking the same is a consequence of having the same actor play him - what exactly were they supposed to do to make him look younger?So Kor bathes more often?
In the end, I ended up having to put the Cardassian lifespan at 150-200 years: not quite as much as a Vulcan, but enough to explain what we saw in "Wrongs Darker than Death or Night."
Wouldn't it suffice to have Cardassians, much like Klingons, reach high physical and social stature at an early age? Very young children were being trained in the art of torture in "Chain of Command". Perhaps Dukat, coming from a good family, was the head honcho of Terok Nor at the ripe age of twenty?
Making him the same age as Kira's mother would put him at sixty in the framing story. He could plausibly be in his fifties for the time we see him in preceding DS9. All we have to believe in addition to that is that he began to look like fifty at twenty already. Unless that was part of the Orb illusion; substitute a younger-looking Dukat there, and you might have realism.
Timo Saloniemi
The former is the only issue here. It would make sense to interpret it as you do - this would certainly explain Rugal (12 years old?!

However - and this is what I mentioned before - James Swallow interpreted it in the similar way as Nerys Ghemor. He said so himself on the Trek Lit subforum, explaining his decision to include Dukat and other canon characters in The Day of the Vipers, which takes place from 2318 to 2328. Since he makes Dukat a young officer in 2318 (and Kotan Pa'dar a scientist of about the same age), this would make both of them at least in their 70s at the start of DS9. (And let's not forget Dukat's wife, who has to be the same age as him as she is also an adult in 2318, married to him and having her first child. We know from DS9 that she had given birth to their son Mekor around 2360.) And he also made the Bajorans long lived or at least very slowly aging - since people like Jas Holza (mentioned in "Ensign Ro" as a Bajoran politician in exile that Beverly met recently and found to be a great dancer), Kubus Oak ("The Collaborator") or Keeve Falor (appeared in "Ensign Ro") are already members of the Chambers of Ministers, and Jaro Essa is a major in the army. Now, if we presume that the they were young politicians, only in their 30s, that would still make them at least 80; if they were about 40, make that 90 years old. Now, Kubus did look older, but not that old, but Keeve did not look any older than 50-something, 60 tops (the actor was 58 or 59 at the time) and was apparently described in the script as "a man in his forties". http://memory-alpha.org/en/wiki/Keeve_Falor
Also, the novels chronologies contradict each other - if you compare the apparent character ages of Cardassian characters in Andrew Robinson's A Stitch In Time and James Swallow's The Day of the Vipers, they just make no sense.