I do not blame you for wanting to wait. I did not get Louie's rabies shot until 7 months and he was still 2.5lbs. I would just be careful not to let your baby around animals that you are not sure of vaccinations. Also, I know there is a law in Louisiana that all pets over 3months have to be given the rabies shot and then a booster every 12 months.
(unless given 3yr. shot) I don't think it's fair to those with small doggies, but it's the law. You can probably use google to find the law in your state.