If such addiction is something that can be diagnosed via a reasonably rigorous procedure, then yes, we'll probably have to do something similar to other addictive things: age limits, clear warnings, maybe even independent ongoing testing of the effects. Compare to selling alcohol.
Is the potential risk of addiction related to why alcohol sale is regulated? Most rationales I've seen for preventing sale to minors relate to health effects and immediate intoxication effects (car crashes etc.) instead.
Don't get me wrong, I'd be thrilled if addictive potential was considered primary among reasons to consider regulating something. I'm just not sure it is.
Most social sites already impose age limitations.