I think your junior is doing fine and he is doing exactly what I want him to do, run everything by me that matters. He is a junior and as he is a junior, my first concern is that he doesn't screw up and very close to my first concern, that he doesn't screw us up. I like the way your junior checks with your senior: better safe than sorry.
Eventually, your junior will be socialized in the ways of the firm and he'll operate on his own, knowing in full what's expected and more importantly, how to do it in ways that are not in cross-prurposes with the ways of the firm. He's not repeating the same questions over and over again, is he? If his questions are all brand new, I'd say that your senior had better answer them.
You're seeing a problem, I don't. In fact, I see a good thing.
Considering all the minor disasters I had to clean up because somebody failed to consult somebody else, I'd say it'd be wonderful to have juniors like him. Your senior is annoyed that the junior is constantly consulting him. Look at it on the bright side, your junior is VERY easy to manage. Just about the last thing you should do is discourage your junior from asking questions. Especially if nobody documents much of anything at your workplace.
I'd seek to built up junior's confidence in their judgement by asking junior: "okay, you asked me but I'm going to turn this around on you. How do you suggest that we attack this issue?" Who knows, junior's idea might actually be better than mine :) If I am satisfied with junior's answer, I'll smile at them and tell them "Okay, you answered your own question. Now, get the hell out of my office :)" If I am not satisfied with junior's answer, I'll point junior in the right direction. Hopefully, over time, junior will get the way we think.
Ability and judgement are not the same thing. I know junior is capable, it's his judgement that I need to have confidence in and I'd say that his judgement is what I need to work with him to develop over time. There are good solutions but those solutions that are appropriate for our context are only a subset of the set of good solutions.