So I got this cactus (start) almost a full year ago. In that time it has done nothing. Ideas of what the problem is! The cactus I got in the same trade is planted next to it has tripled in size.
Some Cactus are very, very slow growers. Being from an arid environment, they are in no hurry. It looks fine.
The one that has grown faster is a Euphorbia. Some Euphorbias grow quite fast--others do not.
So what you have is normal.
As close up of the guy who isn't growing.
The guy who isn't growing is in fact a Euphorbia...I am thinking by the variegation that it is E. lactea, though once it grows an arm I could tell you for sure. Sometimes these start off slow, then just get a good growth spurt. I would check the roots, and make sure your soil is not too heavy. It looks too water retentive to me, needs to be cut with perlite by half. I also prefer clay pots for my succulents, helps the soil dry more quickly.