The whole Galactic Standard year thing was an excuse to explain away a
mistake they made, where Ryouko said she had been imprisoned for 2000 years
yet Washuu was stuck for 5000 years.  Supposedly all the other ages in the
show are Galactic Standard Years, but it would be pretty silly to assume that,
for instance, Aeka is age 50 and Sasami is 20.  You're probably better off
just forgetting about Galactic Standard years except for that one time.