Ideas
You asked "Are there any other indication that he should be a spellcaster?"
Yes, he has a Spellcaster's Strong Bloodline in traits! AND born with glimmerstone. If he is not a spellcaster then why have STRONG BLOODLINE in traits? This is the bug that I am reporting on.
He also has the Sulani Mana trait. Because of this trait I expect him to be able to do the actions related to the Sulani Mana trait.
I expect the traits to have meaning in the game.
Thought that also did'n't guarantee that they are born as spellcasters just that they are passing it on but I'm unsure on that. I'm not an occult player though so I never play with them. Mother also has strong, right ?
Maybe someone else can shed some light on it.
There's some info on it here: https://www.carls-sims-4-guide.com/gamepacks/realmofmagic/magical-bloodline.php
Could you please also edit your first post so the report correctly reflects that the parents are not both spellcaster as this can lead to wrong upvotes. Thank you
You can edit by clicking on the cogwheel in the upper right corner of the screen.