Sorry man. Plants with the same genetics can have different phenotypes, or 'growth characteristics'. Many strains have multiple phenotypes, so you can end up with tall stretchy plants and small bushy plants all from the same seeds. Phenotypes also have an effect on the final result. With some strains the tall pheno is the better producer, on other strains it's the short bushy ones. Some phenos can have a different flavor or aroma compared to another (all from the same seeds). Potency can even be affected by pheno.
So what I'm saying is it's normal. There's no way to tell which pheno is going to have the characteristics you want before you've grown them all the way to the end. The short plant might end up yielding less, but may be more potent and flavorful. The tall plant might have sparse, airy buds and the short one might have compact dense buds and actually end up being the larger yielder, but maybe have a worse taste. Noone knows until you grow 'em out.
This is also why many people keep mother plants for clones, 'cause then all the clones are of the same pheno. It's also why people recommend starting a large number of seeds and then pick and choose the seedlings.
Also, most mj plants reach maturity between 4-6 weeks from seed, regardless of lighting schedule. One of the easiest ways to tell if a plant is mature is to look at it's new leaf growth. If the new growth has 2 leaves that are directly opposite each other (almost like a Y) then it's still immature. Once it reaches maturity, the leaves will start to alternate (each node will have only 1 leaf). It's usually shortly after this that you'll start to see pre-flowers (around the 8-9th node, probably). This is when the plant has reached 'maturity' and can either be put into flower or continue to veg for a larger yield. If you continue to veg, you'll probably still see pre-flowers at every node on the main stem.
My plants have been way healthier on a 20/4 schedule than they ever were on 24/0.
I also refuse to damage my own babies. I don't top or fim, or remove any fan leaves. If I want a larger canopy, I lst. Any form of hst (high stress training; top, fim, supercrop, lollipop, etc.) is going to stress your plants, slowing growth and possibly reducing yield. In some cases it's ok, like MBlazes single fim he does, with so much veg time the small amount of stress isn't that big of an issue. But for most people (and especially if you're trying to finish asap) any stress is a bad thing.
Just my $.02, from my own experience and experimentation.
Good luck,
