Well, since the obvious has already been stated by my friends before me...
Gohan started off as a crying baby, became the savior of the world at, what, age 11? Then he went to high school and suddenly found himself torn between wanting a normal life with a proper education and having to accept his role as one of Earth’s main protectors, and based on the Buu saga/most of Super, it seems a delicate balance he’s had to strike. I know that his father’s SSG/SSB/UI transformations have left him in the dust, but he’s definitely not the same person he was as a child.
Also, I pointed this out elsewhere, but 17 went from being a ruthless killing machine with no compassion to a park ranger with a loving family...he tried to destroy the world in the Android saga, then made the wish to restore billions of lives in the other seven universes after the ToP.