Hi,
It's GOOD to see people under 25 starting to use their free time for something that may eventually benefit the future ... and possibly even make them designers of the next generations of hardware for things like medical and industrial technologies ...
I would highly recommend starting with a version of C/C++/C# ... I'm personally trying to start my programming self-teachings after 25+ years of trying to make the time and design the course to fit what time I DO have ... rebuilding craigslist systems in the meantime.
I've picked up a few books, and ebooks about learning C ...some as far back to 1993, and plan to start them with a simple Pentium III Compaq Armada laptop I got for $10.00 (one book lists the writer uses a Win95 Pentium 100Mhz with 32megs of RAM and a 6Gb harddrive for all of his C coding - UNBELIEVABLE!!) ... {And the MAIN reason I fully believe that a well-coded program can perform just about any set of tasks You'll need, and still fit on a floppy disk}. There are still HUNDREDS of extremely useful programs written in the days of 16-bit Windows / DOS-based systems that simply don't get dloaded anymore, although a simple Virtualachine can become a serious data-processing animal with them.
I'm also planning to use a copy of Puppy Linux and the included Geany editor for any heavy coding I personally do, and to use the other 30+ ebooks I have for things like perl, SQL, Python, etc ...
I also have the Harvard videos dloaded from the "Free learning Initiative" from afew years ago, and am ttempting to build the course materials for that - including the book.
Basically C is the "Handsome twin brother" to assembly language, which runs all computer hardware back to the 90's ... and a LOT earlier ... then it was binary, which Assembly and C are converted to by "compiling".
Once You learn that foundation, You can then move onto other "environment-based" languages like SQL, Python, XML/HTML/etc, Perl, java, and most scripting languages that actually run inside another program installed on the hardware.
G'luck!!