^ There is no testosterone surge at four. That doesn't happen til about 9. But yes, I think it's a starting school thing. Lots of girls also go through a bossy phase at that age - mine did, 'playing teacher' and ordering people around - and I think it must be the way some children make sense of their first experience of being part of a 'herd', having to follow rules all day long, etc.
This is a 'normal' thing, I think, and quite different from an obsessive/compulsive need to order the world so as to reduce anxiety. Having watching my child (and not the bossy daughter, but rather the shy son) grow up with OCD, I'd say it's not always obvious which is which. I would say, though, that if you have genuine concerns that your child might have OCD rather than just-started-school-bossiness, *get an assessment & appropriate support*. It's not something you can deal with using just 'common sense'.