How old does a hen have to be to hatch eggs?

[my first peepers]

I am brand new to all of this...can a pullet hatch eggs? How old do they have to be before they will even think about getting broody?
OR, how old does a rooster have to be to be fertile?

 

[skeeter]

I have a buff orp hen thats only six months old and she is setting on eggs right now