Marianin. The height the plant reaches is up to you. If you change the timing of the lights so it has less than 12 hours of light it will bud at any height. I know people who will buy a bunch of clones late in the summer then put them outside and have them bloom. They might get a 1/4 ounce per plant but when you have a bunch it adds up.

That said letting the plant veg until it is 4 ft before budding out will yield a much larger amount of buds. The longer the veg the greater the yield.

Personally I believe the quality is actually better if the plant gets to be about 2 feet or more before budding.