I got a few questions can anyone help me out?

Im new to indoor growing and i was wondering when my plants are growing and they get to a height that i want can i start the flowering process even if its like 18" tall?

Yes you might have to stake them up and prune the lower 25% but they should be fine. Pruning the bottom might seem counter-intuitive but if you flower taller plants the light has to be raised. The bottoms will get leggy and never fully form into tightly packed calyxes covered with trichromes that we want. I usually clone with this material. You are wasting precious resources if you don't. Trust me you prune for growth trim for beauty.

as long as u have the space and light i dont see y not

ya you can basically flower whenever u can do 12/12 from seed or switch after 3 mon veg just whenever it's convenient for you

wow all 3 at same time haha

hell yea thanks yall

just remember that when you switch to 12/12 your plant is not going to stop growing immidiatly, it will still grow a bit more so leave room for new growth, also if the plant is not matured enough it wont show sex until it is so switching too early can slow down growth and still have to wait 2-3 weeks for the flowering to actually start, generally after about 12-14 inch tall they are mature but not all strains are them same, im just going by what i am growing. i switched to 12/12 on the 7th of december and did not get a sign of sex until about the 25th and they were the males, the females came about the 28th and im still waiting on one to show.