I feel I need one, especially as I'm going to try and do my first real startup, but I don't know where to find such a person.
1) Where do you find this kind of people? Incubators? Posh parties? Shared work spaces? Networking?
2) Should the mentor be a person highly experienced? Or just more experienced than me?
3) I know it's a bidirectional exchange so I have to provide something to have it. How is this really working?
4) And in time scale, how much does a good mentor follow his protegé?
Thanks for any suggestion!
When you're doing interesting things you will meet people who are motivated to help you.
People won't take much of an interest in a person who is looking for a mentor but not doing anything.
Stop overthinking this. Establish relationships with other entrepreneurs near you. You can shoot the shit with them when things are good and when things are bad. You'll get introduced to other interesting people.
One day maybe you'll meet the fairy godmother you seem to be seeking, but if you don't you'll have made a start and know some interesting people. And, crucially, you'll be doing something.
Edit: Just saw that you're based in London. Go to the meetups and hackathons and python dojos and LRUG etc.