Although video game sales have increased steadily over the past 3 years, we can expect a reversal of this trend in the very near future.
Conclusion
We can expect a reversal of this trend [increasing video game sales] in the very near future.
rephrase: in the very near future, video game sales will decrease.
Evidence (and)
Historically, over three quarters of video games sold have been purchased by people from 13 to 16 years of age.
The number of people in this age group is expected to decline steadily over the next 10 years.
Evaluate
The author is assuming that since there will be fewer people in the 13-16 year old age range, there will be fewer video games sold to people 13-16.
But it's possible that 13-16 year olds in the next 10 years buy more video games per person than they use to in years past. So even if there are fewer of them, they might still buy as many video games in total.
The author is thinking assuming that because 13-16 year olds have historically been the #1 video game buying demographic, they will continue to be the #1 demographic in the near future.
But maybe video games are changing. Maybe they're increasingly marketed towards 20 year olds or 10 year olds. It's possible that fewer games are purchased by 13-16 year olds, but because more video games are purchased by 20 year olds and 10 year olds, there are still increasing numbers of video games being sold.
Goal
To resist this Prediction argument, we would want to hear about something that is going to change in the near future that would allow there to still be just as many video games sold, even though there are fewer 13-16 year olds.