Big Brother 99 But they could cgi most of their face to dull the ageing process because there is a quick time jump between (Divergent-Divergent (film)) and (Insurgent - Insurgent (film)) but when it comes to Allegiants part one and two, then that is when they have do cgi a little more. Because of their ages.
But in the book it says that Tris is 16 and Four 18 and they cast a Shai-22 year old and a Theo a 28 year old, they must of done this on a purpose. Like when they castes both Kristen Stewart and Robert Pattinson for Twilight. They must of saw the onscreen chemistry they had with the audition. They had to get along with each other, they ended up getting along and becoming good friends.
Other then that, the age differ should not be an issue, in the book it says when you reach 16 you are a full fledge member of society and that makes them full grown adults. Because I can remember a line that Marcus says while talking to the factions.
On the choosing ceremony. That line just makes more official stating that they are members of our society and what not.
Well accordingly to dauntless, when you find your love, it is permanent, like abnegation. They do not allow divorce, but I think that if they got married in the franchise. They would be ok, because of the age gap should not be a issue. But you can't always help who you full in love with. If they were destined to be with each other, then don't stop them. Let nature take its course. That will be a nice way to say it.
So yeah, that is how I feel about this topic, all I understand about it should be in written in this mini essay written about this topic, and it will give you more insight into the way this topic should be ok and what not. So enjoy.