Most of you are probably aware of Coursera, a platform that offers many university courses for free or very cheaply. They have a very good selection of music courses and today I signed up for these two which are totally free, unless you want a certificate, then you pay a little (about USD $40)
One other thing I've used and highly endorse: getting an amateur radio license. Since the Morse code requirements are pretty much a non-issue anymore in most countries, it's purely a process of learning practical electronics theory and practice. True, this applies to _radio_...but as we all know, there's plenty to do with audio there. Plus, the digital modes get into some of the DSP turf for generating signals AND reception/demodulation of ludicrously weak signals...which requires a serious working knowledge of signal cleanup, noise reduction, etc.
Plus, you're learning an additional skill...and believe me, there is NOTHING like the rush of firing off a puny 10 watt signal (I use lower power due to masochism the challenge it poses for a voice signal) from a wire in your backyard and doing a bankshot off the ionosphere to get it to come down a few thousand miles away. Cosmic billiards, baybee! WX9T AR.
I actually got the bug a few months ago. I have zero experience with electronics and I'm not so young but I thought I'd start. AE modular is probably to thank/blame I liked the thought of one day tinkering to make some modules.
I released the first skill to acquire was math, and this was from basically no skill. I ordered various books. At first it was frustrating but it's been a few months and I'm really enjoying algebra, which surprises me because I'm definitely not a natural and always hated math. I have electronics books ready and have completed some of medium complex formulas once I understand what some of the variables mean. I don't feel that confident yet though. Most of it is still way beyond me.I'm not sure what level I'd need to reach in math just to do electronics. I guess that intermediate algebra skills and then being specific to the electronics formulas would save time in the long run.
I started looking into basic Arduino programming and it's not that bad. I downloaded some PDFs to read and haven't been through them all yet, but there doesn't seem to be that many amazing books about it in my opinion. There is a Youtube channel called Paul McWhorter and he makes it very easy to understand the basics. There are a few Arduino books based around musical projects.