Can you try a little reverse psychology?
As in
" I know that you can make the walk but people are so very rude in airports that they will think nothing of knocking you over in their rush to get to their gates . So taking the assistance is the only reasonable option -etc."
Or perhaps a financial perspective ( this angle worked on all topics with my grandfather)
" to get a reasonable fare I had to book with a shorter connection ( earlier flight, further gate whatever) than I would have liked and it won't leave us time to walk."
Good luck!