I just reached level 19 and now its finally letting me pick perks for leveling up? I play on PS4 and all the 18 level ups before I was only able to pick leveling up with the top S.P.E.C.I.A.L category's. I wasn't able to go down the chart and pick certain perks till now

I was confused about that at first too, I didn't pick any perks until I was about lvl 10. Instead of putting a point in your s.p.e.c.I.a.l spots you can put one in a perk.