I am a 23 year old graduate student in electrical engineering, and I just told my family that I applied to my local seminary for the priestly formation program. Let me tell you how it went. Maybe it will help you.
My dad, who is a professor of engineering, always had dreams for me to be a great engineer, earn a doctorate, and become a professor as well. When I told him, he responded that he was not too shocked and that even while I was studying engineering, he thought I was wasting some other talent that I had. He seemed to understand, and although he is an agnostic, he told me that I had to go “where I hear the music.”
In a twist, my mom, who is a faithful Catholic, tried to get me to reconsider. She wanted me to stick with my studies and eventually get a job in industry.
This is exactly the opposite of what I expected. It just shows you that there is no template that will tell you how your parents will respond. You just have to be honest and tell you father. It will make you feel better, and his response may be surprising. I will pray for you.