According to the Lost Era novels, the ban on women serving on the High Council was instituted after Azetbur's death as a reaction to her rule, to prevent a woman from becoming chancellor again.
Although TNG is inconsistent about whether women can serve on the Council; in "Reunion," Gowron offers K'Ehleyr a seat on the Council if she'll back his claim to leadership. The ban was only introduced later in "Redemption."
This doesn't have to be an inconsistency. After all, what one ruler proclaims can be revoked by another.
Once Gowron becomes Chancellor, he can say that this law is no longer valid and put K'Ehleyr on the Council.
By the way how does a lowly born klingon become a noble? Was that ever shown movie, episode or book?
It's been a while, but I think the "Left Hand of Destiny" books said that Martok was born to a poor family and had earned his 'nobility' -- first in promotion through the KDF ranks to General, then as Chancellor (which he didn't really earn but was meant to be).
Could be wrong, but like I said it's been a while.
Yes, he is - or better said, started - a peasant.
I believe that he gained his Great House by marring Sirella, she was after all "royality". And an officer with potential could have been seen in a good light for a Great House without an heir.
- just my conjecture.