I mean they kinda never tell the ages so we never know
Even if bride is 20 years old seme is still soo old for him he is alive over ahundred years.
This is the one time I actually don’t think that way, to me he doesn’t look young just extremely feminine in nature he doesn’t look like he has done much of hard labour so it could be that he has less muscle mass plus we have already seen him when he was a child, the dragon guy looks not much older then him just more masculine looking and with more muscle on his body and I highly doubt he's over a hundred and even if he is its highly likely that he is still around the same age as Rita in dragon years.
I like it but the "Bride" ML looks so young and looks like a child to be in a yaoi manga.