Alter Aeon Online Help

Keywords are:  'size height'

Your character is created with a certain size, and based on that size may
be slightly better or worse at doing certain things.  There are certain
doors which may be too small for larger characters to easily fit through,
and certain skills which may work better or worse for larger versus
smaller players.

However, the size of your character really isn't very important, and if you
need to temporarily change your size, you can use equipment to do so.  Most
players ignore size completely.