I think the sage advice is to find someone who's doing what you do, but is ahead of you on the roadmap (but not too far ahead, perhaps). How do you do that?
Be experienced enough to know enough people in your field.
Find a contact channel and ask someone you respect. If that fails, ask someone you've already known and respected for a long time. If you can't or won't do that, then you should go it alone. You don't need mentors to succeed.
I find that I know enough people after working for more than a decade that my mentors have become the people I already ask for advice, so making it official was a minor step.
To address your specific requests:
1. Knowing yourself well enough means knowing your blind spots. Anything you dismiss without question is a blind spot. Have mentors who cover them. I have robust conversations with all my mentors, and they always give me pause for thought.
2. Asking for time means you need to focus on what you're asking of them. Mentors are there to advise, not make the decisions for you, or finance your endeavour (unless they already do). Ask politely and they'll say yes.
3. Well-framed questions help, but I find that I won't know the questions to ask until I've experienced something unexpected. Also, sometimes I find some of the best conversations come out of asking open-ended questions. I think there's a time for both.
As to my situation: I've asked mentorship from people younger and older. I've asked friends and acquaintances; some I know well, some I don't. However, they are all willing to be honest. It's necessary that we disagree on some things.
My blind spots are things such as raising money vs. bootstrapping (bootstrapping all the way!); revenue from products and services vs. revenue through finance or advertising (I believe revenue should come from creating material value, not increasing it through financial vehicles); cryptocurrency as a business model (I find few projects are genuinely useful). If the opposite of my belief happens to be useful, then it helps to have someone who understands it.