From "The Hope of the Redoran":

"Many, many years ago, a male child was born into House Redoran"

The boy was named Andas.

"His worst enemy was his cousin Athyn, who had borne much abuse at the hands of Andas."

"Athyn had been sent to Rihad to complete his education"

"When Athyn returned from Hammerfell, it was because of the death of his father, who had also been a councilor of the House. Athyn was old enough to take his seat in the Council"

"Athyn exercised his right to combat his cousin for the seat."

"Athyn and his friends were discussing the duel morosely when one of his old teachers, a warrior called Shardie, came into the hall. "



The book seems to infer that the Redguard named Shardie was an accomplished fighter and teacher before Athyn Sarethi was old enough to take his seat in the Council of House Redoran. 

I do not know exactly how old is old enough to take a seat in the Council, if anyone does please let me know, but it seems to me that Athyn was a relatively young man during the events of this book. 

As far as I know Redguards have pretty much IRL human life expectancy, whereas Dunmer live much longer. 

In game, Shardie appears as a young woman and Athyn as a very old man, this seems highly unlikely to me so this mod changes their faces to better match the lore behind the characters, Athyn now appears younger and Shardie appears old.