From the pics you first loaded, too early to determine sex. I do not see any flowering YET. Plants look VERY healthy. Never go by the lowest / first and even second set of leaves, theu almost alwyas die off. New growth is what you look at and yours is fine. DO not lift the lights...you do not need stretch. If they are true autos, you will see the sex soon. You have a very nice setup going...watch the temps and Rh as you are moving into the next stage very soon. Even though they may be autos, you can kick start flowering by increasing darkness to 12 hours...a week or 2 should do it and then you can go back to 18 or even 20 hrs of light. If they are photo period, keep the lights at 12/12 so you do not reveg. This is the time to concentrate on training (LST), topping, fimming...and soon as you start seeing the sex, you can start feeding them appropriate nutes