So if Godzilla takes place in modern times, and skull island took place around 1974, this is going to be a battle between a youngish lizard and a 60 something year old gorilla?
John C. Reilly's character in Kong: Skull Island mentions that Kong is still young and immature, so I'd assume that his rate of growth is rather slow. He should be in prime adulthood in the timeline of this film.