Board Thread:Naruto Discussions/@comment-30642680-20161215233748/@comment-734582-20161216114450

The only one never truly answered is why he looks even younger, but presumably it's because of his research. He was already busy occupying younger bodies before and presumably managed to create a Shin body for himself.

He also looks androgynous probably because he's inhabited both male and female bodies (IE versus Hiruzen he fought in a female body).

Orochimaru wanted Sasuke for his research into the Rinnegan. (Assuming he at that point knew it was the Rinnegan. it's possible he wanted to do it plainly because a senju-uchiha combo would be powerful).