I am an MSc of urban planning with more than 25 years of professional practice. Can someone please tell me if age is in any way negative for being considered by a top university in the USA or UK for a PhD, especially for international applicants?
No, so far as I can tell, age is not a negative for application to graduate school in the US. But you will have to explain your reasons for wanting to do a PhD and provide some evidence of your interest and ability to do research and that could be harder for you. Admissions committees like to see published papers and letters of reference from academics in a position to comment on your research skills. If you've spent your career in industry, it could be difficult providing that kind of evidence.