S-kyuu Kishi no Ore ga Seiei Butai no Taichou ni Ninmei Sareta ga, Buka ga Minna Toshiume no S-kyuu Onna Kishi Datta

Zeke, a dragon-slaying knight at the tender age of fifteen, is an S-rank Black Knight. He is appointed captain of the elite Dragon Killer Squad, which consists of the elegant female knight Loe, the cool female knight Katia, and the easygoing teacher Flamebelle. However, both Loe and Katia refuse to acknowledge Zeke as their leader and challenge him! Surrounded by beautiful women older than himself, Zeke's harem life begins, with a sweet yet strong-willed heart that knows when to be decisive! (Source: Brave Bunko, translated)