WHEN SHOULD i START FLOWERING?

my plants are about 5 wks old... not too big. when should i start 12/12

That depends in many factors.

We'll need a bit more info to be of any service.

i usuly start after my plants are 36" tall about 7 to 8 weeks but its mostly dependent on how much room you have vertically

This is a very basic question and the answer depends solely on you and your growing environment.

You need to allow the plant to at worst triple in size during 12/12 So you need to take the height of your plant now and triple it and make sure you have enough head room for the light and plants.

Alot of flowering is determined by how much room people have to grow in.

J

it's really up to you remember, they can triple in size when flowering.