No difference
You get permits from the Department of Licensing. That is also where you get an actual license, after you take a riding skills test of course.
15 years and 6 month
Depending on what particular state do you live. Here in California, You can ride a motorcycle w/ a learner's permit ONLY on days and NO passengers and only on your local roads and No freeways.
im not quite sure but i found this = There is no license needed for driving a moped and you can ride from the age of 16 years, so i'm gonna say yes