I deal with eye contact issues every day. Some days i am completely fine, others i need to just have conversations without looking people n the eye at all. They tend to be fine with it
I would suggest asking yourself what emotional gain you are seeking from eye contact, and what emotional need he is seeking from not having eye contact. Then you are weighing what you need versus what he needs in order to feel comfortable. If you are having conversations already, even with eye contact, that is a step in the right direction
Ultimately, you can only make it safe for him to experiment with eye contact. If you force him, he will resent you for making him feel hurt, especially him being young still. He will do it in his own time.
If however, you feel that your need for eye contact cannot be denied, even when you have considered his need for not maintaining eye contact, i would recommend, instead of trying to make him, simply say that you like it when he makes eye contact and that you get a lot from eye contact, but that you won't force him to do it until he is ready and happy. That will prepare the ground for him to take steps on his own. It may take weeks/months, but if you give him space, he will grow into it.
I am no Dr. just someone who has learned to cope. I hope these pointers are useful