A line of ten chiefs + Timmain and a total span of 10000 years does not fit together.
Tanner's chieftime was described as long and peaceful for sure - and he was described as very High One like. He was the only one who visibly aged - hair turning grey included. That's why I decided to make him very much older and grant him a overlong chieftime. (Yup, I know the Wolfrider's Guide says something about 800 years - this time I do not care about it! Had to fix this d*** chiefline somehow