I think manaketes would age till they are matured and then the aging process would drop considerably, i mean we can't expect to believe that like nowi had the body of a 2yr old crawling around for a few hundred years, and Nah is only around 18 and already has the same appearance Nowi has, And Tiki tells Nah how it's difficult living past everyones lives and that she will come to get used to it not to mention Nowi is half manakete. so i think Corrin is a manakete and will live thousands of years :p