There's an undercurrent to all of these that I think should be brought out in clear: don't be combative. Preserve your relationship with him. It's great to take his advice with a grain of salt and validate it in books and on sites like these, but don't attack him. If he's a senior developer and has been through lots of projects, he's not an idiot, and there's lots to learn from him. As it seems like you've already done, express your desire to understand his viewpoint. Even if you're sure he's wrong and you're right, accept the possibility of the opposite (seems like you already understand this). Try to make it clear that you're arguing because you want to understand his viewpoint better, not because you're trying to prove him wrong.

If he doesn't get back to you right away when you ask him a question, or if his answer is vague and/or unhelpful, don't assume he's blowing you off. As has been mentioned here already, he may well be busy and/or stressed.

It's also great to be patient. Keep a list of things in your head that you think should be done differently, and present them at the proper time. Make sure you have justification for the suggestion besides "it's best practice." And be careful to do things right and to not make mistakes, so that you have credibility when you make your arguments later on.