Welcome. When I was your age, I confided that I wanted to "get into electronics" but hadn't made much progress yet. Two friends offered advice that I still hear today. One simply said (with great emphasis and some irritation at my hesitation) "well then, GET INTO Electronics!!" and the other said, "get as much education as you can, it will pay off". Good advice, so I pass these on to you in hopes that you keep going.
In my own experience, I started with a 8085 microcomputer development kit way back many years ago but also played around with an Altair 8800 and PDP11 minicomputers too. The most benefit was the Z80 computer that I learned to do assembly coding on. Using assembler can be a pain, everything is hard, but boy you sure learn exactly how the computer works. So, for that reason, I suggest that, while a BASIC stamp is not a bad start, I would rather see you working with a language that is more connected to the machine than BASIC, like assembler or perhaps C+. Trouble is, it will be tougher to get started as these tend to be more complicated than BASIC but at your age it is a reasonable challenge. With that all in mind, I also recommend starting with a microcontroller development kit. My choice would be the STK500 kit from Atmel ($83 at Mouser), based on the AVR series of micros.
PS: loved your work in Knight Rider