Both have a woman dating a much younger man and struggling - with an older man slowly realising that not only does *he* like her too, but that she is actually a great person and he screwed up in the beginning by not realising it. The only difference is the endings - one has the woman ending up with the older man and the other has the woman ending up with the younger guy (and no, I'm not saying which is which - you'll just have to watch and see!)
Both are comedy-dramas about women in the much-feared around-40 demographic, thought to be the point of no return if a career path is chosen and having a family is not an option society will grant...but these women have a different sense of who they are and what they want in life on their own terms, even if they know they actually can't have it all.
They both have the same concept - three women who regularly get together for 'ladies nights' to discuss their respective love lives and the social pressures (regarding marriage and their ~expiry dates~) for their respective age groups that they're in danger of collapsing under. Tokyo Tarareba Musume specifically targets issues of women "around 30", whereas Otona Joshi specifically targets the "around 40" age group.
Both have an independent career female protagonist who is around-40 and struggles with the dilemma of being successful at work at the expense of her dating life due to societal norms that go against her lifestyle choices. Also, both feature an eccentric and somewhat arrogant male romantic interest who acts like a romance expert and gives advice incessantly, but experiences dating struggles/failures of his own.
