My bulldog didn't go into heat until 10 months, and I have heard of lines of APBTs that didn't hit their first heat until 12-16 months.
And I'm glad to hear you're not looking to breed her yet. Until she is fully grown you can't evaluate her structure properly. Also she would need to have titles on her and all of that good business before even starting to look for a stud. Breeding is a looooooooooong road if that's the one you choose to pick.
"All changes, even the most longed for, have their melancholy; for what we leave behind us is a part of ourselves; we must die to one life before we can enter another." -Anatole France