In every state I'm aware of, brucellosis vaccination has to be given to heifers prior to 1 year of age, with the exception of bangs-free states where the vaccine is not required.
The bangs vacc is a LIVE vaccine, so the reason for it being given prior to one year of age is so that you don't run the risk of bred heifers aborting when the vaccine is given. Anything that's bred or older than 12 months needs to be given a special "cow" vaccine, and it's not easy to get a vet to order it in and administer it - may even require special testing prior to vaccination.
I vaccinate my herd for brucellosis, BVD types I and II, IBR, PI3, BRSV, the 5 strains of Lepto, Vibrio, the standard 7 clostridiums, and redwater.