I work in an industry that is very heavy on engineers in both the younger and older end of the spectrum. I happen to be on the younger end, though certainly with enough experience under my belt that plenty of my older co-workers trust my opinion on technical aspects.
However, I have one older co-worker, let's call him Bob (he appears to be near retirement age, if that matters) that, no matter how technically sound my argument is, will not cede the point. This can be for trivial matters and for more important matters - he seems not to discriminate. Oftentimes, my argument is based on conversations I have had with other, more experienced co-workers who are also proficient, so this isn't just something that I, as a younger engineer, am coming up with off the top of my head.
So far, my only recourse has been to get my supervisor (of an age with Bob) to back me up. Usually, my supervisor makes almost the exact same argument I made previously (not surprising, since often I bounce ideas off of him before talking to Bob). Bob then accepts the argument, and we've all wasted time in the process. Just to note, Bob is not a direct report of my supervisor, and he does not work in the same department.
Now, I can understand having a questioning attitude, and this sort of thing is valuable in my industry. However, I think Bob takes things a little far is disregarding the technical opinions of younger engineers (this doesn't just happen to me). In case you were wondering, Bob does not accept the opinion of two younger engineers who agree on a topic, so it's not that he just wants two people to tell him the same thing.
What sort of approach should I use with Bob to help him see my side of things without always having to have my superior intervene?