I have a 2 year old lab that hasn't been neutered.

I am going to fix him next month because I want to prevent him from breeding, but I would also like him to be more mellow.

Someone told me that it is too late for him to change his behavior, even if I neuter him.

Is this true?

I will fix him no matter what but I do want to start taking him to the beach again, and I want to make sure he is not going to attack a smaller dog.

Thanks
William Scott