There seems to be a great deal of variance in size among corns. It depends on genetics, how often you feed, and what is fed. 18" is pretty big for a 2 month old. Mine was 18" when I purchased her, and she was about 6 months old. However, she's now a foot longer than my other corn that is only a couple of months younger. My larger corn is nearly 3 ft. at about 15 months old. My other is only 26" at 13 months.