Great thread :thumbup:
I'm not sure I can really add much to what's been said before so feel free to ignore.
I started playing guitar at 8 years old by picking up my sister's nylon string guitar. She showed me a few chords from her 'Girl Guide Campfire Songbook' and off I went. I can always remember that THE biggest problem I encountered very quickly was being able to move smoothly between different chord shapes and not have to pause at every chord change to reposition my fingers. Learning how to move efficiently between chord shapes is so important - by that I mean if two chords share the same note, if you can, don't lift that finger off when you change.
I had my first lessons at 9 years old and they were very basic BUT the great thing about them was the level they were pitched at - we learnt a new song every week, just a few chords, simple strumming pattern but I could come home and play a new song to my parents and it felt like I was progressing.
Everyone will have a different opinion I'm sure but personally, I wouldn't get bogged down in any formal notation yet be it tab or stave, if he can strum the chords to his favourite song he's just heard on the tv, he'll be over the moon and then some! I definitely would encourage the use of proper chord names for given shapes and if you use chord boxes that could be a gentle lead into tab proper.
I don't read music and it's never held me back but then I don't play in a pit orchestra and I'm not a session musician. Around the age of 11-12 I moved to another teacher who was a real old school folk guy and learnt lots of fingering picking and had my first exposure to reading tab and a bit like the 'moving between chord shapes wall' I hit early on, I seriously couldn't get my head around 'how tab worked' (not helped, I might add, by the fact that this particular teacher for some reason used a system whereby the fret numbers were written in the gaps BETWEEN the lines :crazy: ) but I can vividly remember sitting on the sofa one day trying to play Ralph McTell's 'Streets of London' and the whole concept of tab just suddenly clicked.
I probably didn't use a flat pick until I was about 14 but I'm a really strong finger picker and I dare say the reverse would be true today for a beginner - they'd probably be given a pick very early on but I would absolutely say don't forget about your fingers !
Everyone learns at different speeds of course and today we're really spoiled with the sheer amount of apps and online content.
I would sound a note of caution about those apps that you play along to that have the cues for the next chord change etc. (kinda like the bouncing ball over the top of the lyrics). I've been giving lessons to a cousin who has picked the guitar up again after many years and he's very keen on them. However, in my opinion, you become so reliant on the visual cue for the chord change rather than listening to the music, that if you take it away, he can't play the song. Even if I was to give him a lyric sheet with the chords printed over the top of the words at the change points and play the original track, he can't play it because there's nothing showing him WHEN to change.
Anyway, enough of my waffle, the absolutely key thing imho is to keep him interested and if he's still playing in a few years he'll probably want to discover all the other technical and theory stuff for himself.
Good luck :thumbup: