Absolutely not an overreaction. For someone to post about gambling at the age of 17 and fraudulently signing up to a poker site to gamble and then for any half sensible adult not to discourage this behaviour in the strongest possible terms would be completely irresponsible.
While poker is a form of gambling, winning players take money from fully aware adults if the site tos are not being broken. As for the argument that winning players profit from gamblers therefore they shouldn't care about dissuading gambling, this is a point of view I cannot subscribe to.
Its one thing to play against anonymous gamblers its another to withhold advice from someone that has posted in our community underage about the possible pitfalls of what they are doing.
If you could wave a wand and magic away every problem gambler the ones that gamble way beyond their intended means then I would be for this regardless of the loss in ev. For someone to post about taking gambling interests to the 'next level' and chasing losses sounds like the start of a very slippery and razor laced slope to me.
So yes I will advise against such behaviour. Laws exist for a reason.