Yeahhh it really does suck. The only saving grace we have is that mentally he was the same age as Ranmaru and physically we don't know how old he truly was. Likely a teenager, but it's not clear, especially since everyone acknowledged he was pretty meaning he may just look younger than he is and retains that beauty longer due to that. Also the body he comes into is one that only exists for him and isn't some random teen he's possessing so blame the universe for that
maybe I hallucinated it, but i think his body was 15-16
but yeah man what a saving grace
it's killing me that it's even more obvious now that ranmaru was so young when they were sleeping all those years ago