Background: I bought a TRS-80 in 1979 and was coding in Z80 assembler before I played much with BASIC. From there, I also tried out the Tandy Color Computer (6809E-based), the Commodore VIC-20, C64, Amiga {500,1200,3000}, PCs starting with 80286's, and so on. I've written assembler for all of the above, so I understand the low-level things. When the TRS-80 went on the fritz, I opened it up and unsoldered one of the 7474 ICs on the board to replace it.

I don't remember how many times I replaced that motherboard -- twice? three times?
I took engineering classes at junior college (A/C and D/C circuit analysis, etc) and got bored with hardware. It was cool, but way too much like "work" for me. I switched to comp-sci and have never regretted it.
Like your nephew, my initial focus was hardware. I added 32K of RAM to my Color Computer by piggy-backing the RAM chips on top of the existing RAM chips, except for the CAS pin and the CS pin, running those over to an unused gate on a flip-flop that had to have its traces cut from the circuit board (Tandy had grounded all unused pins). But there wasn't as much variety in hardware as in software. With hardware, I was limited by the available technology, while software was virtually limitless in its potential.
I now own a consulting company. I spend a week or two a month doing corporate training (teaching OO topics, programming topics, Un*x system administration, and more) and I spend the rest of the month with little consulting gigs here and there.
My advice would be to have him get his feet wet in as many different areas as possible. Have him try hardware, including design, system engineering, drafting, radio frequency, and so on. And some software; really big topics right now are security (encryption, intrusion detection), networking in general, human interface engineering, and so on.
It would be really cool to get him an internship somewhere that would offer a taste of all of these. The FBI (here in the US) would be a good choice, or a defense contractor. Be aggressive: call the HR department and tell them you want to work for free (yep, no paycheck). That will get their attention. Then tell'em what your interests are and offer to work for free for 3 months (or 6 months or whatever you feel comfortable with). Once you've got your foot in the door, ask them for a reference and tell'em good-bye. If they liked your work, they'll offer you a job and you've already got the experience they want. If they don't hire you, you can say that you interned with the FBI, which is a nice thing to put on a resume'.
