As mentioned by others, you are ahead of many of your peers in thinking about the SAT as a 9th grader.
Should you be studying for the SAT yet? Sure, if you have the time, desire, resources, etc...but that's pretty generic. Here's some more specific items which you can do immediately to help determine your path...
1) Speak to your High School Counselor. They are a great resource and at some point you may want to ask them for a reference/recommendation for your college applications, so getting to know them now is a great move. More than likely, you will be able to take the PSAT at the end of the 10th grade. This will give you some good insight into how you may score on the "real SAT," but it means waiting many months, possibly.
2) Sign up for KHAN ACADEMY! It's FREE! https://www.khanacademy.org --> They are the "official" partner of the College Board (folks who develop the SAT). As per Khan Academy's website, "For the first time ever, the creators of the SAT have given Khan Academy exclusive access and advice to build a personalized practice program for anyone..." (We'll come back to Khan Academy in a minute)
3) Sign up for a "College Board" account --> https://www.collegeboard.org/ --> There's a LOT of information out there including what's on the exam, how many questions, how long is it, what's it cost, how it's scored (perfect score is 800 + 800 = 1600 btw) etc...
4) Once you have the above accounts, then you'll want to sign up for the SAT Prep (FREE, FREE, FREE) course in Khan Academy. You can then proceed at your own pace of learning the material...but, self-study is tough and can be daunting...
5) So, sign-up for https://www.schoolhouse.world --> It's (you guessed it...) FREE, FREE, FREE! It's an offshoot from the founder of Khan Academy (Sal Khan) and is a FREE Tutoring service on many different subjects. It has numerous options for SAT Prep, SAT Bootcamps (for when you are getting closer to an exam), etc. Most of the sessions are led by other high schoolers (there's some very caring/giving/smart folks out there).
6) As part of the items above, you can take a "practice SAT." ( You will probably take several during your PSAT/SAT journey) You can see your score and figure out your strengths/weaknesses.. The SAT is a marathon, not a sprint. Just 10 minutes a day for 2 months (basically one less YouTube video a day) adds up to 8-10 hours of "studying" (which is almost a full school day or two, but in bite-size chunks). If you do this for your whole 9th grade year, then you will be much more prepared than most 10th and 11th graders. Consistency is key. Don't make it a hassle, just use some "spare time" to invest in yourself every day.
A couple overall items to note:
a) Studying for the SAT Exam can help you in your overall High School classes. If nothing else, it should give you confidence that you are able to tackle some pretty hard questions. Although, there will be some areas you probably find challenging and will need to spend time to learn/re-learn the material. For instance, if you haven't taken Geometry/Algebra 2, then there will be several questions you haven't learned, yet. Give yourself a break and don't stress over them. Try to learn what you can but realize that you will get better with practice and having taken the classes.
b) KHAN ACADEMY and SCHOOLHOUSE.WORLD are FREE! Most of your high school classes (Algebra/Biology/Chemistry/History/English/Pre-calc/Calc/AP classes, etc.) all have courses on Khan Academy! There's even sections on College Admissions/Advice, Personal Finance and Careers! Most of these also have tutoring sessions available on Schoolhouse.world as well! So, while you asked about SAT Prep (which is on both), one thing you want to do is to have more fun in High School and get good grades. Putting in some "extra effort" by using these sites will help you with the grades and hopefully reduce your concerns/stress so you'll have time for more fun.
Hope this helps!