I can understand the frustration, but BG3 follows D&D rules. Low-level casters in D&D have pretty limited capabilities, including the number of spells they can hold in their heads. In D&D, the idea (for wizards, at least) is that their magic comes from study, and requires mediation to prepare spells. To refresh those spells, a wizard rests.
As you level up, the spells you can learn are way more powerful.
Sorcerers don't have to study, per se, but do have to rest to regain spell slots.
A game that follows D&D rules can be a bit jarring if you're used to a pretty much unlimited supply of magic for your characters. You might have more fun with a mixed class, like a Paladin or Warlock, that combines fighting and magic. But hopefully, if you stick with it and level up, and gather a good party to support you, the magic casting will pay off.
As an aside, I can't speak for the average age of users here, but there seem to be a good deal of us who remember playing BG1 when it first came out, and I'm 57.
