Hi xerox,
Yes, you can postpone making a credits only ESA claim for a year. When you make the claim you can ask to be your son's appointee which means you are allowed to represent him. He may not need a Work Capabilities Assessment as there may be enough " paper based " evidence to make a decision. Also there are long delays reported at the moment for the ESA WCA so you could find yourself waiting almost a year for the WCA medical anyway.
David
Nothing on this board constitutes legal advice - always consult a professional about specific problems