A lot can keep them small. A small pot, poor soil, small light, but the last picture shows mold or fungus damage to the stalk.
Unless you put them in the ground and feed and water regularly, they'll be small. Even then, if it's poor soil, you'll have to dig a good hole and fill it with a supersoil. A good hole is one that is wider than it is deep. So 3' wide x 1' deep is better than 1'x3' deep. The downside to that is that the plant will need support once the buds start packing on weight. But that a good problem right?
Indoor, some experienced growers can get 1 to 1.5 grams per watt (light). Some have mentioned 2 grams, but ... that's stretching it I think.
Outdoor, if you want to grow a 5 pounder, start her in April, transplant often, get her out June 1, and be prepared for a shit load of work. One big plant can overwhelm a new grower pretty quick.