@liu
TL;DR My essay about "My Isekai Essay, By: Bucket" in which I argue that Bucket could have easily learned magic.
You make some interesting points; but I still feel like there would be multiple routes to pursue the occult for our protag.
Ultimately, a lot of the discussion comes down to whether we are talking about a hard magical or soft magical system.
https://en.wikipedia.org/wiki/Hard_and_soft_magic_systems
If it's a system like FMA or Harry Potter; there might be grimoires or formula that are used to practice magic; but certain users would have the knowledge or experience to subvert those requirements. I think this is more akin to what many magical schools teach in our world. Flying Witch is another example of this; where we see magic that is the result of careful reproduced formula; as well as magic that is done on the fly using nothing but willpower. In other words; mediation and knowledge might prove more valuable to our protagonist than materials. Additionally, our protag has read isekai stories himself; which frequently have somewhat researched magical systems worked into their stories. I'm willing to bet he has more magical knowledge than the average person in his world; perhaps enough to cast a spell or two.
Regarding pricing and availability of teachings, I think that too wouldn't be an issue. It's only in his home country that things are ridiculously expensive due to magic being banned. In other countries, it's highly likely that the use of magic would make certain manufacturing processes much cheaper; thus making books more common. Even if the materials were expensive, surely there would be monasteries similar to our world where the teachings would be free through scripture and/or oral tradition. What better time to become a monk than right after being reincarnated? Many of the religions in our world are essentially magical traditions; especially if you look into their roots. I'm sure such religious organizations would exist in his new world given that there is an even stronger basis for religious belief. No entry fee required.
Barring monastics, certainly some wizard of esteem would be interested in a convincing tale of a silicon future. Not only can our protagonist describe in detail the life he lived; he can draw it. I've no doubt that someone would believe him if they themselves practiced magic. It would be nothing like telling the same story to someone in our world, because they already have a basis for magical belief, and thus you would remove a thick layer of skepticism. Wouldn't you be interested in teaching someone who has many years to advance their art, yet a more developed maturity than a child? I think his circumstances are easily worth a scholarship; if not for his story than for the innovative ideas his story represents.
(unless of course reincarnations are ultra common)
This is a good point to segway into the bit about his age. Starting magical training at 30 might be late for someone expecting to live until 60 or even 100. You'd be far behind other wizards at that point, and perhaps hard-pressed to start a standard magical career. But in this instance, I think we can safely assume that extremely long lives can be achieved through either reincarnation or direct life extension. Why not invest in magic if your life is perhaps going to last hundreds of years, if not longer? Even if he didn't catch all the earlier starting opportunities, he finds out he has enough magical ability to use the charm; which would have been a good time to start.
Lastly; even if our protag doesn't pursue magic or know how to do many practical things like creating paper, metal, electricity, etc.; I still think the idea of such technologies would be massively useful if they don't already exist in that world. Their toilets for example will probably run the risk of polluting water systems. If Bucket can explain the basic premise of how that occurs, and how boiling water makes it safer, he can save many lives. Perhaps he doesn't know how to create a safe septic system, but he can get the ball rolling. (Assuming these elements apply to that world)