M.H.
I don't think you need to worry about the toxicity of the vaccine. These vaccines have been around and tested and approved for six month olds. This vaccine is the best way to avoid having him contract a flu that may have serious complications.
However, your doctor should always respect your request to delay or avoid a vaccination. If you feel like he is too young for the vaccine, then it is your right to refuse it. (Hopefully a discussion with your doctor will reveal this, and the receptionist just came across wrong.) There are a number of vaccines recommended at the next few appointments, and it may be worth while discussing a schedule for them with your doctor.
One thing you may consider is asking whether you and your husband can be vaccinated. By protecting yourselves you are avoiding bringing flu into the home, and thus protecting him. If you take this route, you may wish to avoid bringing him to enclosed spaces during flu season (indoor playgrounds, etc.). And, of course, wash hands when you return home, etc.
The vaccine may not be available then - no one has it in stock right now.