Do auto flower plants grow faster naturally because I always see people taking pictures of them being 21 days old and they're MUCH bigger than any normal plant that would be 21 days old.
Autoflowering cannabis has a very brief vegetative stage, some as little as 1 or 2 weeks. Most autoflowering strains begin flowering by week 3. Cannabis will grow 2X-3X its size during flower, and in some cases the growth can be downright explosive. Photoperiod cannabis is usually kept in a vegetative state for longer, so the growth-spurt of flowering is delayed (intentionally). Peace!