I agree with what everyone has said so far. What type of boa do you own? A lot of dwarf type boas are more aggressive naturally, so they take more work to tame down. In all my years of owning 100’s of boas, females are more aggressive than the males I have owned. My wife says that’s a female response to me, 
However, almost all of my boas are very tame. Only a handful were very aggressive and took a year or two to tame down. I own 50 boas right now and only 2 boas I don’t trust yet. Both are females. Will probably take me a year to tame them to where I will trust them. They are both 4 and 5 years old now. They started getting aggressive around 2 and 3 years old. If I only owned a few boas they would have been tame by now. I just don’t have time to work with them like I should.
I have also noticed when I breed a semi aggressive female boa, the babies tend to be more aggressive than tame female babies.
Has anything changed in your boas environment or at your home, such as a new pet dog or cat? Maybe children playing around the cage more now? Do you breed your own rodents? If you are breeding rodents they should not be anywhere near the boa. If you can have the rodents in an out building or in your garage. I can’t tell you how many people I know tell me their snakes are always aggressive and it ends up they keep rodents near there snakes. Snakes all have a very excellent sense of smell. My boas and retics go into feeding mode as soon as I bring in my frozen rats from the garage.
Boa constrictors can make good pets for the right owner because they are generally calm, long-lived, and relatively low-maintenance once their habitat is set up properly.
Also, captive-bred boas often become quite tame with regular, gentle handling and are less prone to defensive behavior. Hook training helps with this. Start this from when they are babies. Gently tap their head or body with a snake hook. Every time you go to take them out of their cage or cage cleaning day. Don’t use the hook on feeding days. They will associate the cage opening and hook training with interaction with you and tolerate handling well and can become calm, predictable pets when socialized.
Never restrain a boas head with your hands as they don’t like this at all. Remember, a restrained boa is a mad boa. I know I don’t like being held by my neck or head.
When handling your boa, do not have a death grip on it. Let it go where it wants for the most part. Just hold them loosely but in control of them and let them move around and change your hand position by going hand under hand as they move around. You can still direct it so you have control of it. Never put your hand directly towards its face. Always guide under it’s chin and a few inches back from the neck. Keep it moving, and it will not have time to think about biting you.
If your boa stops moving, they may start thinking about biting. So keep them busy with moving around.