I think the adult market exists, and it will keep growing as the people who grew up with games become adults.
Here's why I think the market doesn't exist..
Adults arn't satisfied with the games..
Most of the older guys buying the new games don't even have the time to play them..
They stack up in their steam catalog..
yes the momentum of having played games as a kid has come through some what..
But these games are still failing to actually capture an adult's attention.
A fundamental divide between adults and children is that, most adults work in the real world, for money, and they begin to realize how precious their time actually is.
This makes a digital excursion seem extremely expensive. So the payoff relative to other things such as "food,sex,alcohol" is much smaller per unit of time.
Which is why in truth, games have not truly penetrated the adult market.. Even though more adults have purchased games for themselves than in the past.