Is it a helpful method to use with older people? Are there any issues to bare in mind? I am specifically thinking about indoors (home) walking interviews and if anyone had any similar experience?
The best anthropologist I know on this approach is Jennifer A. Dickinson at University of Vermont. She used this approach in her dissertation research in Lviiv, Ukraine. Her dissertation is entitled "Life on the Edge: Understanding Social Change through Everyday Conversation in a Ukrainian Border Community". You can visit her research webpage: http://www.uvm.edu/~jadickin/Research.html.
I don't know of any research that specifically looks at using the method to interview older adults, but I do know of a great practical guide by Andrew Clark and Nick Emmel that is even available as a free download online: http://eprints.ncrm.ac.uk/1323/1/13-toolkit-walking-interviews.pdf
I know interviews are being conducted on older people in the EPIC study in Norfolk. The interviews are on exercise rather than just walking but you might be able to gain some insight from this work. Please go to http://www.srl.cam.ac.uk/epic/
The Health Sciences School at UEA does a great deal of research with older people and may have covered similar work to that which you are planning.
Former colleague of mine at the University of British Columbia is just writing a up her dissertation and she conducted walking interviews with older adults - I don't think she has publications out on it yet but has published extensive on older adults and mobility devices. http://scholar.google.co.uk/citations?user=bj5M46IAAAAJ&hl=en