Thanks for the replies. It seems there is a good deal of variation about how much/little students using AoPS are able to self-teach, and/or need teacher or online instruction. I guess we'd need to try it and see what works for my ds.
In regard to the above 2 quotes from Julie and snowbeltmom, I would not say my ds yet "feels empowered by math discovery," or "wants to devote a great deal of time to math each day." He's solid in math, is starting to enjoy the puzzle-solving nature of it, and is appreciating what math can do for him (via programming and robotics). I think he's going to be more of an applied math person, than a theoretical math person. My ds averages about 90 minutes a day on math, but wants to get it done ASAP. At 12yo/7th grade, he does get frustrated easily, but comes around and retackles the task after he's had a chance to cool off. I'd say this is more developmental than math specific, but he wouldn't naturally have a cheerful "willingness to struggle." He's very pleased when he gets a tough problem correct, and likes feeling accomplishment. Would you recommend AoPS for someone described this way?