Right - 17 year olds are unlikely to have enough experience of business or negotiation to know (for example) what conventions protect themselves from exploitation.
But, on the other hand, can learn that as quickly as anyone else.
The amazing thing is that Silicon Valley doesn't take advantage of young founders in this way (at least much less than in the East Coast/other environments I've seen). YC did a lot to change the culture of VC in Silicon Valley — I think almost everyone has shifted to playing infinite iterated games where screwing over a newcomer is disadvantageous because you don't know where they'll go in the future.
But, on the other hand, can learn that as quickly as anyone else.