Will getting my older dog fixed affect his health?

hes a pitbull hes never been aggressive or roamed or anything so i never saw the need to mutilate him in that way but now they made it a law in my city that he has to be fixed he is about 12 years old and i need to know if it will affect his health. will he heal ok? will it change the way he behaves? he is still quite active and playful some people say male dogs get lazy when there fixed and have no energy