You don't think that in an advanced age like this, that they don't have superficial body modications even before the age where they can get genetic body modifications?
Also, if they are manipulating their DNA, it stands to reason that even young children's DNA is optimized before they are born, thus giving them better physical attributes. Especially if you consider that splicing requires the mother to extract eggs in advance to maintain her fertility. Those eggs are likely sequenced and optimized before they are re-implanted.
As far as story continuity goes, there seems to be an in-world explaination for this which is not obviously found in other stories other than cultivation tales.
