Board Thread:Questions and Answers/@comment-5774380-20150511135448/@comment-5774380-20150511140738

My answer is SPOILER, so if you are not up to date to the latest chapters, do not read below this line. :P

Rod hinted that the shiters' Titan forms are created looking for a specific set of characteristics, so its probably that the Colossal Titan has that size because it was created for that reason. And as Locket answered in the original post, he is not the only Titan that large. The Wall Titans have similar heights, and Rod himself is twice as large in his Titan form.