Plant Gender and Pollination

How do you properly sex a plant? At what age is a difference apparent?

Do I need a male for a female to produce buds? Or is a male only needed for seeds?

Do male plants produce buds too?

I have seen male pollen for sale online. How is it collected from the plant?

You can put a whole tray of seedlings in 12/12 for about 4 days to sex them, then revert to normal vegging if you have many plants.
Males are only needed for S1 seeds. Females can make seeds all on their own though sometimes.
Male plants produce tiny little flowers and pollen sacks that are no fun to smoke.

You can also take cuttings and put it under 12/12 to see what it is.

Some say you can sex a plant in vegetative state, but I find i have to change them from 18/6 to 12/12 light cycle and after 4-7 days the pistils (female white hairs) become apparent.
You can avoid all this by buying feminised seed though.
Nobody needs or wants males except breeders. If I got a male in my grow room I would dispose of it sharpish to avoid it pollinating any females.So no, you don't need males around. (This made me think of chickens, for some reason...)
Males don't really produce anything at all worth smoking. Most growers see them as a hazard.

I have 7 seedlings that are just starting out. How old do they need to be to do this?
What will the visible differences be? Right now my biggest seedling is about 2 inches tall. i have 4 that just shed their shells today, and 2 about to break ground. They are regular, unfeminised seeds. I have them on 18/6, fluorescent while i wait for my big green & bloom LED to arrive. Once its here I will transplant into pots and finnish setting up my tent