Ok young lady, it's time to listen to the old man (who has done more of these trips than anyone else - including UC). I grew up in Europe (Germany & Ireland) and know the differences between the continent & the U.S all too well. I've traveled from Munich all the way to Greece to Turkey to Egypt to Morocco to Spain to France & back to Munich on a moped when I was 16 years old. I've traveled from NYC to Atlanta & back hitting every park along the way. I make multiple trips from NYC to CP & back every year, hitting up parks along the way. I travel to Canada & back multiple times a year. Not to mention my annual two week ski trips where I go to a different resorts (in multiple states) every day. In other words - I won't give your anything but proper advice.
As many have stated, a rental car is the only way to go. I don't understand why you need to have someone older with you because I was renting cars here in the U.S at 23 years old without a problem, it will just cost less to have a more experienced driver rent it for you (but money isn't a problem, right?). And driving over here is a breeze compared to Europe (less traffic and wider streets). It will also cost less when renting a car for longer periods of time (compared to daily rates) & you can get a GPS with your rental (a must). Drive the car everywhere except your flight to Los Angeles (rent another car there).
Since your are planning on staying a month, that will give you plenty of time to do the parks and take a day off here & there to see some of the country. Plus you will be able to do the East Coast, Midwest & Los Angeles (but I won't recommend trying to squeeze in Texas as well - save it for next time).
Here is the itinerary you should consider (added an extra day in case of unforeseen circumstances - as UC mentioned):
Day 1 - Fly to Chicago
Day 2 - Buy a Six Flags season pass & do Six Flags Great America
Day 3 - Drive to Cedar Point, buy a Cedar Fair Platinum Season Pass & do Cedar Point at night.
Day 4 - Do Cedar Point & drive to Columbus, OH
Day 5 - Do Kings Island & drive to Louisville, KY
Day 6 - Drive to & do Holiday World (spend another night in Louisville, KY)
Day 7 - Drive to Knoxville, TN (rest day)
Day 8 - Do Dollywood
Day 9 - Drive to & do sightseeing in Atlanta
Day 10 - Do Six Flags Over Georgia
Day 11 - Drive to Charlotte, NC & do Carowinds
Day 12 - Drive to Williamsburg, VA & do Busch Gardens at night
Day 13 - Do Busch Gardens & drive (1 hour) to Ashland, VA
Day 14 - Do Kings Dominion & drive to Washington DC
Day 15 - Do sightseeing in Washington DC (do Six Flags America if you're a coaster whore)
Day 16 - Drive to Philadelphia & do sightseeing
Day 17 - Drive to & do Six Flags Great Adventure, dive to NYC
Day 18 - Do sightseeing in NYC & ride Cyclone (do Rye if you're a whore)
Day 19 - Drive to Boston & do sightseeing
Day 20 - Do Six Flags New England & Lake Compounce (a must)
Day 21 - Drive to & do Dorney Park, drive to & do Knoebels, drive to Hershey, PA
Day 22 - Do Hersheypark & drive to Pittsburgh
Day 23 - Do Kennywood, drive to & do Waldameer (a must)
Day 24 - Drive to Niagara Falls & sightsee, drive to Toronto
Day 25 - Do Canada's Wonderland
--- (extra day can be used anytime up until now)
Day 27 - Fly to & do sightseeing in Los Angeles
Day 28 - Do Disneyland & Disney's California Adventure
Day 29 - Do Six Flags Magic Mountain
Day 30 - Do Knott's Berry Farm & Pacific Park & more sightseeing
Day 31 - Fly home
* You get free entry last 3 hours at Hersheypark if you purchase a ticket for the following day. Only do this if you're ready to leave Knoebels, but skip it if you love the park as much as Ben.
You can squeeze days 11-13 into two days if need be. After Carowinds drive to Richmond, VA to spend the night & do Busch Gardens the next day. Driving from Atlanta to Richmond with a stop at Carowinds along the way will be a very long day, but I have done it twice. :wink:
Paying for two full days at Busch Gardens and only getting a day & a half sounds crazy, but I think it's worth it because the park is amazing. I do it all the time, but then I have a season pass.
As you can see, there's plenty of days off from parks sightseeing in cities that have plenty to see. Atlanta is The South, Washington DC is beautiful, Philadelphia is historic & edgy (South Street), NYC is the capitol of the world, Boston is dope, Niagara Falls is gorgeous & Los Angeles is Hollywood baby!
There are a few double park days in there, but all are a must.
SFNE isn't a full day park & Lake Compounce is only an hour away. Plus Lake Compounce offers reduced after 5pm tickets & you're only there to whore Boulder Dash (especially at night!). Lake Compounce is a very small park & you can ride all the other rides in a hour.
Dorney Park is on the way to Knoebels & is a small park. You can ride all the coasters & be on the way to Knoebels by noon. Knoebels is also a small park & having most of the afternoon/evening should be enough time to take everything in. The parks are just over an hour apart (75 minutes or so).
Waldameer is 90 minutes from Kennywood & there are only four rides, but one of them if Ravine Flyer II. You can get your fill of Kennywood before 5pm & make it to Waldameer by 7:30pm. The rides at Waldy are ticket based (no park enrty fee) & the drop tower (although small) is one of the very best. So ride Comet & Dragon once, then whore RFII & the drop tower until closing time. RFII is da bomb at night!
Knott's is not a full day park & Pacific Park is just a coaster & Ferris wheel on the Santa Monica pier, so no problem doing both & then some in a day.
The Six Flags season pass will get you into every Six Flags park and you'll need the Cedar Fair pass for Cedar Point, Kings Island, Kings Dominion, Dorney Park & Knott's Berry Farm. So you'll save a ton of money buying both those passes. Make sure you get the platinum passes for all parks, which cost a bit more than the single park passes.
So there you go. The trip of a lifetime all mapped out for you. Look it over & let me know what you think. :--D
P.S. - Sorry for not keeping it to 15 parks.