First, what is your bodyweight right now? If you are asking about hitting depth on squats that means you probably aren't (especially because of age) so your one rep max or 320 may be off. Are the numbers you listed as one rep maxes with or without gear? Are your projections with or without gear? Either way, going from your total to what you want in 6 months is a hefty goal. You are young and probably can get much stronger faster than I can but that is going up a lot in your lifts.
On bench I would say to read articles by tate or wendler on benching. Retracting your shoulder blades is something you can do whether you have a narrow or wide grip, it is not dictated by the width of your hands. You have got to get used to doing it every set, every rep and it will take over like anything else.
On deadlift hopefully you are using a mixed grip instead of a double overhand grip. If you are going double overhand then take one hand and flip it around. That will help a lot if you are like me.
On squats train them to parallel every rep, every movement. This has always been what helped me. I always hit depth no matter the weight. A box helps some people, some people prefer to be called up at the meet. I don't like to have to "feel" for the depth so I always train to depth and have no problem doing the same at the meet. Most good lifters know when they are sacrificing depth for weight, I'm not sure if you are in that category. You have to take a reality check and maybe take your weight down to start training proper depth.
Sorry if I come off negatively but you have a ways to go if your lifts are raw and your projected lifts are raw. A change of gear can always help along with tweaking your form. Get someone to coach you and learn your commands early. Start implementing them in training early so you don't have to worry about them the day of the meet.