
What's there age difference?

I guess the seme is around +/-25. I didn't read the Lightnovel about his youngest brother, but from reviews etc. I remember that the third Shouto brother was 23 and at that time Keiki was having those parties to search for his fated pair. So Ξ±No Hanayome must take place around or directly after that lightnovel.
I will miss this manga