I don't think you can pinpoint a time when grey hair became a symbol for wisdom - I'd bet it's been a pan-cultural assocaition since time immemorial. Just because, especially in days of yore when people were not expected to live past forty, a grey-haired person would undoubtedly have seen a lot of things and amassed many experiences and therefore was regarded as being "wise".
Griseldis is AWESOME and so is
Grizel, ohhh my gosh.