Are boys really "all boy"??

Our first is a girl (8 years old) and very outgoing but sensitive. Has always been very easy. We're due with a boy in 3 weeks and I'm terrified haha. Everyone keeps telling me boys are "all boy" and rowdy etc etc. When I'm around all my tiny boy cousins and they're running around like mad, it gives me serious anxiety about it! So if you have a boy already, do you find this to be true? Or do you think boys are often this way because parents assume they will be and are more lax on discipline/telling them to settle down etc? Help!

Ugh ps I totally didn't mean to post this in the baby names section! Sorry!