Hey RallyEX,
So you're coming to visit California. To be the best of my knowledge, not a whole lot goes on in Irwindale. Depending on when you are going to be here, you will have the opportunity to visit our
L.A. county fair. It's very large (as many fairs are) and has plenty of things to do.
Beaches: Huntington tends to be very busy during the summer, but you may luck out a bit father south (Newport area). PCH has sooo many good places to eat that you usually can't go wrong. I'm sure other will have more knowledgeable opinions on this subject. Speaking of PCH, it is a very scenic route, if you want to go for a nice relaxing drive. It can get a little busy around the more populated areas depending on your time of day and day of week.
As a person who shares your fear of heights... I love flying. It's the coolest thing. I've never felt uncomfortable looking out the window. For your first time, you may want to take the aisle seat. If you are prone to motion sickness, ask your pharmacist about something to help you out.
Rental cars: In my experience (being 21), you can usually pay a small insurance fee and be allowed to drive a vehicle when under 25. This may change from one car rental facility to another, so don't quote me on it.
If you've got any more questions, shoot away.
And have a good trip!