What they wrote would be exactly as valid or invalid as it is now. Account age (education, job title, etc) does not magically validate (or invalidate) ideas, they have to stand on their own.
> if they had a two year old hacker news account, how exactly would that change the content of their post?
The likelihood of astroturfing would be far reduced. (That would indeed be playing the long game!)
Compare that to this post, it isn't about the posters personal experience or testimonial, they claim none, it is objective points, not a personal testimonial about how "Uber saved my life 7 weeks ago..."
http://www.ftc.gov/sites/default/files/attachments/press-rel...
... so I stand by my initial point, when you CAN have a rational debate, DO have a rational debate. When you can't -- you are right to call astroturfing, no way to argue with how people feel or unsubstantiated personal claims.