Ah yes, the classic troupe in doujins where the milf is always sexually frustrated.
That trope exists for a reason. Most women go through a period in their early 30s where they're extra horny. Unfortunately, men around the age of 30 are often career-focused and their sex drive starts tapering off. It's worse in Japan, since a man in his early 30s will have a lot of work responsibilities and the work-life balance is garbage.
When we were in our early 30s, I'd joke with my girlfriend that we needed to find her some young, dumb 18-year-old she could bang on the side. I just couldn't keep up.