Is there any reason I can't roast a pullet?

You don't have one. Your children are allergic to chicken fumes. Your oven is made of green cheese. Many possible reasons, but who knows if they apply?

being that it is a young bird and weighs less, there is less meat to bone ratio and it will cook more quickly and therefore dry out more easily. best to keep an eye on it and use your instant read thermometer.

Absolutely not! It'll be delicious.