why waki didnt get old at all,he exactly looks like when he was young

well he tell his story that he in some point realise that he never age and he dont know why he have some theory (〜￣△￣)〜and even the akami live by his blood iread this one ages ago so i hope that help (●'◡'●)ﾉ

i got it now thatnks for helping