That really depends on his interests: A Raspberry Pi board is a computer that one can conveniently attach things to and control them from software. He could b

That really depends on his interests: A Raspberry Pi board is a computer that one can conveniently attach things to and control them from software. He could build a variety of interesting systems with it. A FPGA board would allow him to design digital circuits. He could, with enough skill, create his own custom CPU and computer from scratch. That's a fairly stiff challenge for even college juniors in a computer architecture course.