Reiko Seo just came across my radar. Supposedly she started doing porn after age 50. Still a great body and outstanding nipples!
I really like her too, especially this work of hers.
Reiko Seo
[IRO-048] Married Woman Slut Train: Touched Fifty Mother

I might as well mention another delicious MILF from this series, Kaji Fumina, aged 43.
Kaji Fumina
[IRO-046] The Pervert's Train, Where They Play With Nipples

A good addition to this series would be the husband riding on the same train, for a close quarters/encounter NTR scene.