true, but it also depend on strain, my 80% indica don't stretch more then double at max, and also depend on grow method used
I like to let em mature as a minimum
as a rule of thump (also depend on strain) they are considered seedlings for the first 2-3 weeks, then they will use +4 weeks to mature, when the plant start to set randomly side shoots instead in set`s
it will in most case`s also show sex here with a few white hair`s
wait until that or later if you want the most yield from one plant, if plant count is`t important, you could also go 12/12 from seed with multiply small plant, some like that, I don't, I like em to mature, matter of taste I believe, so anything from 0-12 week`s is considered "normal" indoors and most do sumthing in between