Is There Anyways To Find Out My Sex Before Flowering ????

Can I Find Out What My Plants Sex Is When Its Young Or Do I Have To Wait Awhile. Is there a certain height i can tell at or any other way. Cause i have 2 plants 1 is a baby and ones already like 8 inches with nice leafs. But im hoping to find out the sex of my big one cause im not sure if its male or not and if my baby is female i dont wanna get a pollen on it or ill be screwed.

And also what is a good height to start topping my plants someone told me like after 6 nodes

A Node is a section of 2 leaves that start out everytime a new tip grows right ?

since you are going to top it you can take a clone off of the top of each plant and put it under a light ,away from your plants, on a12/12 cycle.
the clones will start to show sex as they root. you just get rid of the clone and plant its from if the clone is a male.

If the plant is mature enough it will preflower and you can tell the sex of it that way. If its also mature enough to show its sex then you can look really close at the nodes with a magnifying glass and try to determine that way. Yeah about 6 nodes is the right time to top your plants.