Board Thread:Theories/@comment-27821571-20160815111819/@comment-5774380-20160815194820

So far we have three Titan Shifters whose mindless and Shifter forms have been seen: Ymir, Eren and Frieda. All of them follow the same pattern: the mindless form is emaciated, the Shifter form is muscular. Besides that, there are very few noticeable changes with the only exception of Eren's form, which seemingly "grew up", from an initial childish form to an adult form.

We have also Reiner's and Bertolt's forms which did not experience any noticeable change in the 5 years that passed since their first appearance, though we haven't yet seen their mindless forms, and it must be noted that they are also very different to any other Titan seen.

And finally, we have Armin, with an emaciated mindless form, and the Shifter form is yet to be seen.

So taking all of this into account, my theory is:


 * 1) The only effect that eating a Shifter causes in the appearance of the original form is some toning up, but besides that the form remains the same.
 * 2) The Titan form grows up more or less proportionally to the human form.
 * 3) Reiner's and Bertolt's forms didn't "age" because they are a different class of Shifters.

According to the labels in the Titan Serum and Rod's statements, there are indeed different types of Titan forms, with Armin's stated as a "Normal Titan", which is probably also the case of other more human-looking Shifters like Eren, Annie, Grisha and maybe Frieda; while Reiner's, Bertolt's, Zeke's, and probably also Ymir's are a different class.