distance depends on where you are coming from and the route you are taking obviously. if you look in the socal sections of the boards there is a ride from the sfv to sb in a day and taking the train back.
in the ventura/oxnard area it's a little more difficult than just going up pch.
100 miles in a day can be really easy, some folks around here do a century almost every week. if you haven't done one and are carrying a lot of stuff it might be more difficult.
it's relatively safe
are you camping or staying in a hotel?
over 20 years ago when i was 14 or 15 a friend and i rode from malibu to refugio beach about 30 miles north of santa barbara it was about 100 miles and took us about 10 hours with no maps and getting a little lost here and there. if a couple of dumb kids on crappy ten-speeds can do it, you can