I have my own theory, which is pretty proven for me, that every human being forms his personality in very early ages of its life. It is amazing to see photos of some people who are in their 30's or 40's and to compare them with the photos of them while they were very young, almost babies. You will see that the most of people do really look like the same they did when they were young.
The skin or hair color and similar things may have changed a little bit but the look of eyes seems to be pretty same in most of cases. Of course this cannot be applied to everyone because some people do change.

The amazing collection of following photos made by combining old and new portraits of different people should amaze you when you see that all of them look almost exactly like they have looked while they were young. The photos were made by New York based professional photographer Bobby Neel Adams who also has created a self-portrait using this technique.
Image credit: Bobby Neel Adams