Yeah that's why they were all eager to kiss him and acted as if it was nothing, turns out the main character is actually more skeptical about having to kiss them than the actual girls.
He stopped turning into a fifteen year old after he along with his friend defeated one of his dad's best friends to free three students (one of them being the one that has a crush on his fifteen year old self) that just followed him and his group without any knowledge of magic. After that the girl found out that he was his teacher but older and he didn't find a need to be fifteen anymore, said girl still kissed him as a ten year old later on though.
He stopped turning into a fifteen year old after he along with his friend defeated one of his dad's best friends to free three students (one of them being the one that has a crush on his fifteen year old self) that just followed him and his group without any knowledge of magic. After that the girl found out that he was his teacher but older and he didn't find a need to be fifteen anymore, said girl still kissed him as a ten year old later on though.