Responses
He's 3/4 years older than and in this time skip she 12/13 so that would make him around 16/17 even so I never consider 3 to 4 year age gaps in manga pedophilia considering, it's littleraly the norm. (for example in the manga "my husband hides his beauty" the fl is 12 and the ml is 14 alothough this isn't really a good example of the age gaps, but if you read many isekai manga you'll know that most of them have 2-6 year age gaps within the male and female lead. (Background characters included.))
Duke/Prince Castillo has white hair and blue eyes but he was in a magic disguise which changed his hair to black. He looks so attractive with both black and white hair (▰˘◡˘▰)
In the present time, he's the one who accidentally heard lippe sing for the first time near the lake, gifted her a miniature grand piano, and danced with her (became her "first dance partner" hehe) on her birthday (ch98).