Prisha,
First welcome to the ACA forums!
I too crossed the country on ACA's TransAm (TA) route when I was 17 during the summer between my Junior and Senior year in High School. It was a fantastic experience and I learned a lot about our country. It was, and still is, easily one of my top 3 major tours after 40+ years of touring (I started when I was 14). It was truly a life defining time for me. I learned the country is not as bad as the media made it out to be. I saw abject poverty, I saw great wealth. I learned in a way that you rarely succeed (get the day's ride done) except through planning and persistence and that no matter how bad things go (cold rained for day and the only grocery store on that day's ride was closed so went without food for a day), that bad things tend to pass. Biggest lesson was that generally speaking, people just want to have a job, care for their family, and be safe. I have found this to be true in all my travels throughout the world. I learned that America has an incredibly diverse topography. I learned as a 17 boy from Oklahoma used to summers with 100* temperatures that it can actually snow in places in the lower 48 in July! Until that time, I would have not believed it.
Your route is not a bad route with the possible exception of Death Valley and Vegas. This is primarily due to the heat which I am guessing would be late July or early August. The highs can get way up there and it is no place to by cycling as a relative novice in the summer. For instance, today in mid-July, the temperature is 118* in Death Valley. Two out of the next thee days the temp is expected to top 125*. Las Vegas is about 115*. Not an ideal time of year to ride there. You can always do Vegas and Death Valley later when the weather is more conducive.
There are some groups out there that cater to teens and early 20s, or at least there used to be. Most do it in some combination with service projects, i.e. they ride across the country and stop in towns and help build a home for Habitat for Humanity. I don't know the names of any off the top of my head but others will probably chime in. They tend to be more expensive overall for some reason but then if it is what you are looking for, it may be worth it to you and/or your parents. ACA also has group rides though they tend to go on very specific routes, i.e. only the TA. If you decide to do this, I would check to see what the demographics are. While I had not issues at all riding with those "old" people over 30, you may not want to. Also, I would guess a lot of ACA tours may be frequented by that age just because the cost is prohibitive for many young people.
As far as your 60 miles per day goes, that is an average amount to ride. However, remember that is an overall overage so if you ride a few 45 mile days because of the way services (lodging, food, etc.) is laid out, you will have to do just as many 75+ mile days to average out to 60. Factor in a rest or short day due to sight-seeing, mechanical issue, rest, parents fly out to see their daughter, etc., once every 7-10 days the miles go even higher. In your 4000 miles in 75 day outline, you don't say how many riding days you will have.
While you can do more than 60 miles per day, I would encourage you to try to keep 60-62 miles per day as your upper overall average with no more than 70 as your riding average (only count the days you ride). I have done as few as 33 and as much as 69 and can say that after 40 years and tens of thousands of miles of touring that, for me, the sweet spot is around 52-57 overall or about 60-65 riding. Obviously, others are happy to crank out 80+ miles so everyone is a bit different. I bet if you did a poll of people who crossed the country without too much time constraints, their preferred averages would be pretty close to mine.
Honestly, if I were you and/or your father, I would strongly encourage you to piece together any of the ACA routes you like to create your own route. The routes have maps and GPS data that are created by and for bicyclists. They are researched with safety, cultural, scenic, and service aspects. They are really good maps, especially for someone getting started out in touring. Each Route is made up of segments. You can purchase only the segments you want to create a customized route.
As far as racially charged encounters go you obviously can have stuff happen to you anywhere you are at any time. That said, I honestly think that the further you get west, the better it will get if stay away from the south eastern USA. It is generally agreed upon in the cycling community that Kansas is the friendlies followed by Indiana with the upper central plains states close behind. The more difficult states are in the southeast and metro northeast. Of course, people can be friendly or unfriendly in any state. Out west, people rely on each other much more than they do in the heavily populated eastern portions. While you may be different, as long as you do go in trying to change them or their way of life, you should be fine. By this I mean, even if you are an avid vegetarian, do not go into the ranching country and start saying how cruel, mean, uncaring, etc. people who raise cattle to be slaughtered are. You are just going to piss them off. As far as being a POC, there are already a lot of POC working the fields in farming & ranching country.
And by listening to them, you may come to appreciate different views. If asked a question they may not like the answer to, just play dumb. If the subjects of politics, religion, or other major divisive topics come up, be vague. For instance, while I am a strong conservative, I avoid talking about politics in general but especially in the more liberal parts of the country I ride in. If asked, I give a vague "I just try to do live my life and not bother others" or "I don't think about it that much" type of answer. While I do not think I will probably be attacked, I just figure what get into a disagreement with someone I will only see for a few minutes and it just may leave a bad taste in their view toward cyclists.
As your parents have probably told you, you are female and too young. While that is true to a certain extent, being young and female is a definite positive in some aspects. For instance, when I was younger (or my kids who do bike touring by themselves), people would be more willing to help than now that I am in my 50s. People generally are willing to help those that are perceived as vulnerable as opposed to those that are not. I regularly tour with others who are in their late 70s. If we need to camp in a town that has no campgrounds, we send the eldest woman to ask. We rarely are turned down with a 79 year old woman asks for help but if I ask, I get about a 50/50 chance since I am 55 (I "should" not need help.). My 40s were the worst.
If I were your father, the biggest factor I would consider is how mature and responsible you are. At 17, I was pretty responsible. When my daughter did bike touring with a friend at 17, I was not "too" worried (as a parent, you will worry no matter what age you are) as she was/is quite mature and sensible. When when she went backpacking in South America for 2 months by herself, I was not "too" nervous. But when my son toured solo at age 21 from Edmonton to Cabo San Lucas, I was much more worried cause he did not have the common sense our daughter did. Luckily he has matured and the solo bike trip actually helped greatly and actually travels the world frequently without too many mishaps.
Basically, if you were truly mature and fairly responsible
and you followed the ACA routes,
and you had a GPS tracker (so I could follow you at all times

in real time in case of emergency) I would not have too big of an issue with you going. Yes, I would prefer you go with 120 other people with a police and ambulance escort on closed roads but you have to make choices in life.
As far as a mentor goes, ideally, you should try to find a woman who has years of experience riding who also started as a teenager. You can also ask over on CrazyGuyonaBike.com. CGOAB is probably bigger forums than here and there may be some woman who can assist you. If you are unable to find someone and/or if your parents want to speak with me as someone who did ride across the country at 17 and has kids who did ride when they were young, I am willing to assist in any way I can. If you do, private message me. BTW, you should probably remove your email as the spam bots can capture it and you will get a bunch of junk mail. Once you private message people, you can exchange private emails.
As far as bike clubs, just type in your town and bike club into Google and see what pops up. If you live in the countryside, search on the biggest towns. Also, ask the bike shop for suggestions as they would probably know.
Regardless of what you end up doing, bicycle touring is a wonderful experience and can be an addictive hobby so be forewarned

.
Tailwinds, John