Thanks for the additional information. It is helpful. He is absolutely beautiful.
The first thing I recommend is a complete physical including imaging for hip issues and arthritis. Also have a thyroid panel run as hypothyroidism can cause sudden aggression. Other symptoms of hypothyroidism can include hair that breaks off easily or sheds excessively. You can read more on medical causes of sudden aggression here:
I'd also have his hearing and eyes checked. He may be startled and acting aggressive as he can't see as well as he used to or hear as well. This might startle him into acting aggressive until he can tell who it is.
If he doesn't have any medical issues, then it is strictly behavioral. For behavioral issues, I'd recommend starting up formal obedience training so he again sees all the humans in the house as the boss. It doesn't have to be with a trainer but does need to be a set time set aside just for training. The reason you are doing obedience training is so he gets used to obeying your commands and becomes more submissive again to you. Dogs that are submissive to humans do not reprimand them which is what growling and nipping is. The following site is helpful in helping owners train their dog. Be sure and click on the link to the page on obedience at the bottom. and links on subsequent pages leading to detailed instructions.
Training works best if you train at least 30 minutes a day (two 15 minute sessions). I would start making your dog work via the Nothing in life is free program (NILF). It is outlined below.
All humans in the household should participate at one time or another. I would also teach the dog to avoid the baby. If he is growling at the baby now, then it is to show his displeasure and warn the baby to stay away, but as the baby gets older, the dog might start reprimanding in a more physical manner such as a nip. So you have to stop this now.
I would start teaching your dog to stay a certain distance away from the baby. You will leash your dog and if the dog gets within 3 feet of the baby, you will give the dog a short tug on the leash and a firm, low toned NO. Since he hasn't been kept away from the baby, it may take a bit of training before he realizes that he is no longer allowed near the baby. Once he starts stopping the required distance from the baby, start rewarding him with a tasty treat like a thin hot dog slice. Don't use boring normal treats. At this point you will see him stopping long before he gets to the baby. It is important that you reward this behavior with both treats and praise. Once he has it down pat, you can start sometimes just using praise and sometimes treats so he doesn't know if he is getting treats or not.
At this point, you will want to teach him to move if the baby gets within 3 feet of him. So you will move the baby into his space and then using the leash move him away from the baby the required distance and give a treat. Since he already know he isn't supposed to be close to the baby, it may only take a couple of times before he sees that he needs to get up and move if the baby enters his space. Since treats are involved, they usually learn quickly. Again, treat for desired behavior. This is important because when the baby starts walking everywhere, the dog needs to move out of his way.
Most of the dogs that I have trained have learned within a few weeks but the owners worked with the dogs daily and were very consistent. Once the baby is around 3 years of age, then the baby should be able to say sit and down with a little conviction. At this point, you will start the baby giving the dog known commands to teach the dog that he has to obey the child as well.
I'd also recommend giving him a crate to sleep in. You can have it in your room. This will be his safe place where he doesn't have to worry about people stepping on him, getting too close or startling him. it can be a safe place. He won't need to worry about any other dogs either. You also have to make sure no one bothers him in his crate and teach the baby not to go near the crate. That is the dog's special place.
I do suspect that he has a medical issue and likely the result to fading eyesight, hearing or a thyroid issue. Get those checked out but in the meantime, start training. Training never hurts and I always recommend teaching dogs to avoid babies and young children.
I hope this information is helpful to you. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have . If you do find this helpful, please take this opportunity to rate my answer positively so I am compensated for my time.