realize/have realized

[Unregistered]

Dear teachers.

I would like to know if there is any difference between (1) and (2).

(1), Now that I've grown up, I realize how important it was.
(2), Now that I've grown up, I have realized how important it was.

[Mister Micawber]

(2) is unnatural in this case, since you have just mentioned 'now', placing the action of 'realizing' squarely in the present. To make (2) natural, change it, for instance, to:

(2a) Since I have grown up, I have realized how important it was.