When should I be starting to prepare my USMA packet?

There is a way for enlisted to go to west point. You will need to get to your unit and talk to them about getting recommended and endorsed to go you need to be in good shape with no dependents and under a certain age I think it is 21 but I could be wrong.

As COL Halvorson said, the USMA admissions page will have the information you need. You will be eligible to apply after graduating BCT. If attempting to apply for the Class of '23, it would be best to start this summer and no later than the end of the year.
Remember that you need a solid endorsement from your chain of command, which can be tough for a new Soldier, especially if you attempt to apply from AIT. Don't be discouraged if it doesn't work out this year. Take the SAT and ACT if you haven't already, and Soldiers are encouraged to apply for congressional nominations as well, although it's not necessary.
As a Soldier who recently went through this process, feel free to reach out if you have any specific questions.

SPC (Join to see), get on the interwebs and go to the USMA home page. All the information is on there. You've missed the submission deadlines for this year. Look at the applications pages and make a plan for the next year. You've got some work to do to get everything ready and you will need your Command's tacit support to make it all happen. USMA is desperate for enlisted applicants, but you still have to meet the requirements.