My rott recently started to growl and bark at strangers....
My male rott Diesel has always been very good around other dogs, and strangers. I socialized him as soon as I got him at 8 weeks old.
He is now about 23 months old and has just now started aggressively barking/growling towards strangers they approach him to pet while we are on a walk or run, or in petsmart. He even growled at a young boy the other day on a walk wasn't even approaching him. He has never done this before.
I am now semi worried to have him around strangers out in public. He never ever growls at my wife or me though. He knows I am in charge. Any suggestions. I appreciate it.
Your Rottweiler is approaching adulthood and his guarding instincts are kicking into high gear. It also sounds as though he's having a lot of trouble distinguishing between people you need to be protected from, and those you don't - so he is over-reacting and growling at everyone. This isn't acceptable and could lead to dangerous behavior.
It isn't a reflection on his individual personality or that he's an 'aggressive' dog as such, more that he's in need of much more guidance so that he can learn what is appropriate behavior. I'd strongly recommend that you get him enrolled in a dog obedience class or have some one-on-one sessions with a professional dog trainer so that you can learn how to show Diesel what is expected of him and rein in this behavior now, before it becomes a real problem.
Do be careful when choosing a trainer, make sure that you find one who is familiar with large, guardian breeds and who understands that they don't need heavy-handed training or punitive measures. Rotties don't respond well to 'tough love' and need positive, reward-based training.
In addition to the training, you need to increase Diesel's socialization experiences, but as he's a bit hyper-reactive right now, you will need some hands-on help from a trainer before you start this. That way you'll know the right way to correct your dogs behavior and how to help him overcome his difficulties right now.
I hope this helps some and wish you lots of luck.