How often has she done young guy/ mature woman?

Were there more than Class and Harvest Moon?

Class (1983) which came across somewhat sleazier than Harvest Moon.

Bisset played her first sexy "older woman" (at 25) in The First Time (1969).

THe years have been kind to her as they say, her wikipedia page has two interesting photos, the 2002 pic looks better than the 1989, mainly due to the clothes and hair styling being different.