I would expect video games sales to go up for quite the while. It's an ever expanding user base.
Video games really became popular in the 80's. So basically anyone both in the late 70's and later grew up with the video games. Any older then that probably thinks there for kids. I figure anyone who played them as kids aren't going to give 'em up at the drop of a hat. They make alot of adult orientated games now as well.
So really You've got a long while before the children of the 80's die off, but you keep adding new generations of kids to the customer pool every year.
It's really wierd that line of generations before and after videos games existed, but the further we go time, the further that line gets pushed.