when I started taking lessons at an eventing barn I was doing cross rails in hunters and jumping NO higher. I took 2 lessons a week for about 2 months, and then she had me ready to do a tadpole 3-phase. I think it all depends on your instructor,your horse, and your drive, because i'm also a sophomore and i'm so motivated that im learning extremely fast. But the horse I took lessons on was a VERY seasoned eventer,so that helped. Now I have an OTTB that me and my instructor are training for eventing, he knows flat and jumping already, but im prepared for it to take a while to move up the levels with him.
At the eventing schooling shows, the lowest level i've seen is pre-ameoba, which is 12". Then amoeba 18", tadpole 2', etc. At horse trials, they start at beginner-novice 2'6"
I hoped this helped!