Works either way, maybe GeniCore didn't care since there's only one way to go in a spacesuit anyway, maybe they wanted them to be the absolutely perfect ideal little girls so they trained them. Either way is feasible, tho different dynamics - both trying to train her because she hates being teased for using her diapers, or her having to get used to diapers and ask every time to be let out and having to trust her owner to grant her that.
Ideal would be 6-7 years, old enough to have a grasp of some thing but young enough to be babied.