SPOILERS: According to Kurt Russel the younger version of himself as Ego was mostly make up and not CGI. It seems amazing what they can do these days with special effects and the Guardians of the Galaxy Vol 2 had a very life like younger version of Ego (Kurt Russell) in the earlier part of the movie. If it in fact is true that it was make up that made him younger it was an outstanding job of deception. You really thought you were looking at a younger version of Russell.
See Guardians of the Galaxy Vol 2 and see for yourself. Now in theaters by Marvel Studios