Hmmm... I would be surprised if age was the issue, to be honest. Firstly, 51 isn't old! Secondly, Change and Procurement experts are in huge demand at the moment, so perhaps you aren't presenting your expertise in quite the right way. I suggest you speak to a reputable agency to get their take on your CV. The fact that you think you could fit in both sectors might confuse recruiters, who could be thinking "Well, which one is he?", and rejecting you on the basis that you have extensive experience, but not enough in either field to qualify you as an expert. And I know that some of the big six are more than happy to take people from industry backgrounds - possibly not Accenture and IBM, but certainly the others - PA, CapGem, Atos and Deloitte.