You'll have to convince his parents by imagining yourself in his/her place.
I feel my biggest loyalty lies with the world at large, and the potential I have to make it a better place, to reach as many people as possible in my lifetime and leave them better than I found them.If you want to truly honor your loved ones, go out in the world and live your absolute best and brightest, make the most of that gift your parents gave you. And you have to be okay with the fact that they may always resent you for doing so, and you have to forgive them that resentment.The alternative is for you to live your life the way your parents expect you to and never reach your dreams. And if you do that, it’s not just you who suffers, but everyone who stands to benefit from the gifts your best self has to offer.
So, we all know pursuing your field of interest is always better.
What most people conveniently ignore is the fact that our parents have 'been there, done that.'
They might not understand the reason behind your inclination towards the field but you will always need their support and encouragement.
With regard to your question as to what he can become, I suggest that he could study literature, become a historian or a geologist at a broad level.