When to start ranking ?

So im level 48 or something and Ive been playing normals and like most of People like me sometimes I 1v9 and sometimes I shit my pants, I played my placements last season as soon as I could I won 3/5 and I was placed in Iron, even tho I had a good performance, does the level affect or something, because I want to climb this shit

My objective is plat this year, Idk if I can but Ill try