Will having herniated discs (and other back problems) at 20yrs old prevent me from staying in the army?

I had back issues after a training accident at Quantico. I had planned to go USMC, as you can see that didn't work out. Had an absolute blast in the Navy. My point is have a fall back plan.

The issue becomes does your back issue prevent you from physically doing the job required of you. If the answer is yes, then you are going to have problems. If the answer is no, then you should be fine, and you need to focus on keeping your back healthy.

A couple of things I found out the hard way after much pain:
1) Stretch your hamstrings. Took many chiropractors to help me figure out that the hammies are really important.
2) Do yoga core strengthening stuff. It really does work. Look anywhere online for a routine. Do it religiously.
3) Stay on the light side. I lifted weights a lot, and it added mass. Probably not smart. Stay lean.
4) See a chiropractor regularly. They should be authorized, and in the military health system. You don't have to pay out of your pocket, like I did...
5) Look into some alternative supplements. I use aloe vera juice and numeric to keep inflammation down. Really wish I had heard about this when I was your age.

I was a consultant on neurosurgery though I am only a nurse. I studied lots of clinical articles the doctors write, and went to their conferences. I also had a slipped disc before I enlisted, and have a sort of similar problem as you now in my neck the last few years, and have had some treatment for it by a very good spine specialist. My first year in the Navy, ortho doctors on the ward looked at my xrays and said, from what we see, we cannot even tell if you are in pain. Since they liked me they said if you report pain, we will recommend your not being suitable for combat positions. I did not take them up on it.
None of your diagnoses indicate any evidence that anything is already pinching any nerves. If you do not take care of it, it could get worse. Posture, not slouching, walking upright, not often looking down at a cell phone or computer, will all strength your core inner back muscles that keep the spine in good shape. It is not as important to build muscles that you can feel and see. Don't do sit-ups more than you have to - though that builds muscle, it can also strain the core muscles. Some instructors teach Pilate exercises - very good for core muscles. Ask a doc if you can get some training from a physical therapist. See these instructions https://uhs.princeton.edu/sites/uhs/files/documents/Lumbar.pdf from Princeton University Athletic Medicine

Once in they can gradfather you in..but when you reach 30% rating your barred from enlistment with that condition..i tried to re-up in 07 when they raised the enlistment age..denied. i am service connected with same injury..trust me. Pt will be murder on that ... tread carefully and get informed before doing anything.