18
You do this when you are 18 and have a passport.
Illegal immigration
You have to be an adult. In most places that is 18.
Yes, it is illegal for someone to keep your passport without your permission. Your passport is considered your property, and no one has the right to withhold it from you. If someone is holding onto your passport against your will, you should contact the relevant authorities for assistance.
No.. Even though your a European citizen you must produce a passport at port of entry..
What exactly do you mean by "individually"? Assuming you're asking about a US passport: Minors are required to have their own individual passports, but a minor must apply in person with both parents/guardians; they can't get a passport without both parents knowing about it and approving of it.
Without parental consent, yes. You can actually get a passport long before you turn 18, but it will require your parents to process it for you. Once you're 18, you can do it entirely on your own.
No, as both signatures are needed for a passport.
yes
of course
If you are a minor you cannot travel without your parents authorization.
A better question might be what possible legal/moral justification do you have for accessing someone else's passport details. There's no way I know of to get them other than to ask the person the passport belongs to, and this is exactly how it should be.